Black colorant for ink-jet printing ink, ink-jet printing ink, and aqueous pigment dispersion containing the black colorant

ABSTRACT

A black colorant for ink-jet printing ink, has an average particle diameter of 0.001 to 0.15 μm, and comprises:  
     extender pigments as core particles;  
     a gluing agent-coating layer formed on at least a part of the surface of said core particle; and  
     a black pigment coat uniformly formed on at least a part of said gluing agent-coating layer.  
     The black colorant for ink-jet printing ink exhibits not only a high blackness and an excellent tinting strength, but also excellent dispersibility and light resistance in spite of fine particles

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a black colorant for ink-jetprinting ink, an ink-jet printing ink and an aqueous pigment dispersioncontaining the black colorant, and more particularly, to a blackcolorant for ink-jet printing ink exhibiting not only a high blacknessand an excellent tinting strength, but also excellent dispersibility andlight resistance in spite of fine particles; an ink-jet printing ink notonly exhibiting excellent dispersion stability and light resistance, butalso being free from clogging at a head portion of an ink-jet recordingapparatus; and an aqueous pigment dispersion containing the blackcolorant.

[0002] In recent years, the development of various OA devices such aspersonal computers has rapidly spread in both business and domesticapplications. An ink jet printer as one of recording apparatuses forthese OA devices has also been widely used owing to the recent tendencyof a low price and a high performance thereof.

[0003] Upon practical use, it is important that the ink jet printershave a higher reliability and a broader applicability. To meet therequirements, ink-jet printing inks used in the ink jet printers havebeen required to be free from clogging at a head portion of theprinters, and exhibit an excellent dispersion stability, a high printimage density, excellent water resistance and light resistance, or thelike.

[0004] Hitherto, various dyes have been used as black colorants forink-jet printing inks because of nonoccurrence of clogging at a headportion of the printers, a good dispersion stability, a good chroma anda good transparency. However, these dyes have problems due to toxicity.In order to solve the problems as well as satisfy the recent requirementfor light resistance of printed matters, it has been attempted to usepigments instead of the dyes. As to this fact, Japanese PatentApplication Laid-Open (KOKAI) No. 11-131001(1999) describes that “ . . .Dyes have problems such as poor water resistance and light resistance ofimages printed therewith owing to inherent properties thereof. To solvethe problems, it has been attempted to develop inks using pigmentsinstead of the dyes”.

[0005] When the black pigments such as carbon black, etc. are used as ablack colorant for ink-jet printing inks, it is possible to form printedimages having a high image density as well as excellent water resistanceand light resistance as compared to in the case of using dyes as theblack colorant. However, since 80% of the ink-jet printing inks aregenerally constituted of water, it has been difficult to disperse carbonblack having a hydrophobic surface as well as organic black pigments inan aqueous medium. In addition, since the pigments are usually insolublein water, etc., unlike the dyes, it has been difficult to preserveink-jet printing inks using such pigments at a stable condition for along period of time, and there arises such a problem that a head portionof an ink-jet recording apparatus tends to be clogged therewith.

[0006] On the other hand, if the particle size of the black colorant isreduced, it will be expected that the ink using such a black colorantcan be prevented from clogging at the head portion, and can be improvedin transparency. However, the black colorant having a small particlesize tends to cause problems such as poor dispersibility in inkcomposition, low light resistance of ink using such a black colorant, orthe like.

[0007] Conventionally, there are known ink-jet printing inks usingpigments (Japanese Patent Application Laid-Open (KOKAI) Nos.9-227812(1997), 11-131001(1999) and 2000-53901); colorants prepared bycoupling pigments with resins particles using a coupling agent (JapanesePatent Nos. 2903631 and 3097208); and colorants prepared by bonding dyesonto the surface of silica particles through a coupling agent (JapanesePatent No. 3105511).

[0008] At present, it has been strongly required to provide a blackcolorant for ink-jet printing ink, which is not only excellent intinting strength, light high blackness. However, conventional blackcolorants have still failed to satisfy these requirements.

[0009] That is, in Japanese Patent Application Laid-Open (KOKAI) Nos.9-227812(1997) and 2000-53901, there is described an aqueous ink-jetrecording liquid containing pigments and colloidal silica for thepurpose of obtaining high-quality printed images. However, the pigmentsexhibit a poor dispersibility in an ink-jet printing ink composition, sothat the resultant ink-jet printing ink fails to exhibit a gooddispersion stability and a sufficient light resistance of printed imagesthereof. In addition, since a large amount of the colloidal silica notcontributing to coloring is contained in the ink composition, it isdifficult to sufficiently increase the pigment concentration thereof,thereby failing to obtain high-density printed images.

[0010] In Japanese Patent Application Laid-Open (KOKAI) No.11-131001(1999), there is described an ink-jet recording liquidcontaining pigments adhered with fine particles of silica or bariumsulfate. However, since an adhesion force of the fine particles onto thesurface of the pigments is very weak, the fine particles tend to bedesorbed from the pigments when dispersed in the ink-jet printing inkcomposition, so that it has been difficult to obtain an ink-jet printingink having excellent dispersion stability and anti-clogging property aswell as excellent light resistance of printed images thereof.

[0011] In Japanese Patent Nos. 2903631 and 3097208, there is describedan ink-jet printing ink, in which the particles prepared by reactingpigments and resin particles using a coupling agent are dispersed. Sincethe coupling reaction is conducted in a solution as shown in thebelow-mentioned Comparative Examples, a sufficient shear force cannot beapplied to the pigments. Therefore, it is difficult to disperse theblack pigments in the form of fine particles, thereby failing touniformly adhere the pigments onto the surface of the resin particles.

[0012] In Japanese Patent No. 3105511, there are described particlesprepared by adhering dyes onto the surface of silica particles through asilane-based coupling agent. As shown in the below-mentioned ComparativeExamples, since the dyes are adhered onto the surface of silicaparticles, the obtained colored silica particles fail to show asufficient light resistance.

[0013] Further, in Japanese Patent Application Laid-Open (KOKAI) Nos.11-323174(1999) and 2001-11339, there are described iron-based blackcomposite particles comprising black iron oxide particles or black ironoxide hydroxide particles; a coating layer formed on the surface of theblack iron oxide particles or black iron oxide hydroxide particles,which comprises organosilane compounds obtainable from alkoxysilanes, orpolysiloxanes; and a carbon black coat formed on the surface of thecoating layer. However, as shown the Comparative Example mentionedlater, since the iron-based particles as core particles have a specificgravity as high as 4.3 to 5.5 and the amount of the carbon black coat isnot more than 30 parts by weight based on 100 parts by weight of thecore particles, the obtained iron-based black composite particles have ahigh specific gravity. Therefore, it may be difficult to obtain anink-jet printing ink having a sufficient dispersion stability when theiron-based particles are used as a black colorant therefor.

[0014] As a result of the present inventors' earnest studies, it hasbeen found that a black colorant having an average particle diameter of0.001 to 0.15 μm and comprising extender pigments as core particles, agluing agent-coating layer formed on at least a part of the surface ofthe core particle, and a black pigment coat formed onto at least a partof the gluing agent-coating layer, exhibits not only a high tintingstrength and a high blackness, but also excellent dispersibility andlight resistance in spite of fine particles, and is suitably used as ablack colorant for ink-jet printing ink. The present invention has beenattained on the basis of the findings.

SUMMARY OF THE INVENTION

[0015] An object of the present invention is to provide a black colorantfor ink-jet printing ink, in which black pigments are adhered onto thesurface of extender pigment through a gluing agent in the form of auniform adhesion coat while being kept in an extremely finely dispersedstate, and which can exhibit not only a high tinting strength and a highblackness but also excellent dispersibility and light resistance inspite of fine particles.

[0016] Another object of the present invention is to provide an ink-jetprinting ink exhibiting not only excellent dispersion stability andlight resistance but also being free from clogging at a head portion ofan ink-jet recording apparatus.

[0017] A further object of the present invention is to provide anaqueous pigment dispersion containing the black colorant for ink-jetprinting ink.

[0018] To accomplish the aims, in a first aspect of the presentinvention, there is provided a black colorant for ink-jet printing ink,having an average particle diameter of 0.001 to 0.15 μm, comprising:

[0019] extender pigments as core particles;

[0020] a gluing agent-coating layer formed on at least a part of thesurface of the core particle; and

[0021] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer.

[0022] In a second aspect of the present invention, there is provided ablack colorant for ink-jet printing ink, having an average particlediameter of 0.001 to 0.15 μm, a BET specific surface area value of 15 to1,000 m²/g, a specific gravity of 1.3 to 3.0 and a blackness L* value ofnot more than 22.0, comprising:

[0023] extender pigments as core particles;

[0024] a gluing agent-coating layer formed on at least a part of thesurface of said core particle; and

[0025] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer in the amount of 1 to 500 parts by weightbased on 100 parts by weight of said extender pigments.

[0026] In a third aspect of the present invention, there is provided ablack colorant for ink-jet printing ink, having an average particlediameter of 0.001 to 0.15 μm, comprising:

[0027] extender pigments as core particles;

[0028] a gluing agent-coating layer formed on at least a part of thesurface of said core particle;

[0029] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer; and

[0030] an outer coating layer formed on at least a part of said blackpigment coat, comprising at least one material selected from the groupconsisting of anionic surfactants, nonionic surfactants, cationicsurfactants and polymeric dispersing agents.

[0031] In a fourth aspect of the present invention, there is provided ablack colorant for ink-jet printing ink, having an average particlediameter of 0.001 to 0.15 μm, comprising:

[0032] extender pigments as core particles;

[0033] a coating layer formed on at least a part of the surface of saidcore particle, comprising at least one compound selected from the groupconsisting of hydroxides of aluminum, oxides of aluminum, hydroxides ofsilicon and oxides of silicon;

[0034] a gluing agent-coating layer formed on at least a part of thesurface of said coating layer;

[0035] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer.

[0036] In a fifth aspect of the present invention, there is provided ablack colorant for ink-jet printing ink, having an average particlediameter of 0.001 to 0.15 μm, comprising:

[0037] extender pigments as core particles;

[0038] a coating layer formed on at least a part of the surface of saidcore particle, comprising at least one compound selected from the groupconsisting of hydroxides of aluminum, oxides of aluminum, hydroxides ofsilicon and oxides of silicon,

[0039] a gluing agent-coating layer formed on at least a part of thesurface of said coating;

[0040] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer; and

[0041] an outer coating layer formed on at least a part of said blackpigment coat, comprising at least one material selected from the groupconsisting of anionic surfactants, nonionic surfactants, cationicsurfactants and polymeric dispersing agents.

[0042] In a sixth aspect of the present invention, there is provided anink-jet printing ink comprising an ink base solution and black colorantfor ink-jet printing ink, having an average particle diameter of 0.001to 0.15 μm, comprising:

[0043] extender pigments as core particles;

[0044] a gluing agent-coating layer formed on at least a part of thesurface of said core particle; and

[0045] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer.

[0046] In a seventh aspect of the present invention, there is providedan ink-jet printing ink comprising the black colorant as defined in anyone of first to fifth aspects and an ink base solution

[0047] the amount of said black colorant being 1 to 20% by weight basedon the weight of the ink base solution.

[0048] In an eighth aspect of the present invention, there is provided aaqueous pigment dispersion comprising a base solution for the aqueouspigment dispersion and 10 to 40% by weight of black colorant for ink-jetprinting ink, having an average particle diameter of 0.001 to 0.15 μm,comprising:

[0049] extender pigments as core particles;

[0050] a gluing agent-coating layer formed on at least a part of thesurface of said core particle; and

[0051] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer.

[0052] In a ninth aspect of the present invention, there is provided anink-jet printing ink comprising a dispersant, water and a aqueouspigment dispersion comprising a base solution for the aqueous pigmentdispersion and 10 to 40% by weight of black colorant for ink-jetprinting ink, having an average particle diameter of 0.001 to 0.15 μm,comprising:

[0053] extender pigments as core particles;

[0054] a gluing agent-coating layer formed on at least a part of thesurface of said core particle; and

[0055] a black pigment coat uniformly formed on at least a part of saidgluing agent-coating layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056]FIG. 1 is a micrograph (×50,000) of silica particles obtained inExample 1;

[0057]FIG. 2 is a micrograph (×50,000) of black pigments used in Example1;

[0058]FIG. 3 is a micrograph (×50,000) of a black colorant used inExample 1;

[0059]FIG. 4 is a micrograph (×50,000) of a simple mixture of silicaparticles and black pigments used in Example 1;

[0060]FIG. 5 is a micrograph (×50,000) of black pigments C used inExample 17;

[0061]FIG. 6 is a micrograph (×50,000) of a black colorant for ink-jetprinting ink obtained in Example 17; and

[0062]FIG. 7 is a micrograph (×50,000) of a simple mixture of silicaparticles used in Example 1 and black pigments C used in Example 17 forcomparison.

DETAILED DESCRIPTION OF THE INVENTION

[0063] The present invention will now be described in detail below.

[0064] First, the black colorant for ink-jet printing ink according tothe present invention is described.

[0065] The black colorant for ink-jet printing ink according to thepresent invention has an average particle diameter of 0.001 to 0.15 μmand comprises extender pigments as core particles, a gluingagent-coating layer formed on at least a part of the surface of therespective core particles, and a black pigment coat formed onto at leasta part of the gluing agent-coating layer.

[0066] As the extender pigments used in the present invention, there maybe exemplified silica particles such as silica powder, white carbonparticles, fine silicic acid powder and diatomaceous earth particles,clay particles, calcium carbonate particles, precipitated barium sulfateparticles, alumina white particles, talc, transparent titanium oxideparticles, satin white particles or the like. Among these extenderpigments, silica particles are preferred in the consideration of goodblackness of the obtained black colorant for ink-jet printing ink.

[0067] The extender pigments as the core particles may be those havingany suitable shape such as spherical particles, granular particles. Inthe consideration of good dispersion stability of the obtained ink-jetprinting ink, spherical particles or granular particles having asphericity (average particle diameter (average maximum diameter)/averageminimum diameter; hereinafter referred to merely as “sphericity”) offrom 1.0 to less than 2.0.

[0068] The extender pigments as the core particles have an averageparticle diameter of preferably 0.0009 to 0.14 μm, more preferably 0.002to 0.11 ,μm still more preferably 0.004 to 0.09 μm.

[0069] When the average particle diameter of the extender pigments ascore particles is more than 0.14 μm, the obtained black colorant maybecome coarse, so that the ink-jet printing ink obtained by using such acoarse black colorant may tend to be deteriorated in dispersionstability, and cause clogging in a head portion of an ink-jet recordingapparatus. When the average particle diameter of the extender pigmentsis less than 0.0009 μm, such particles may tend to be agglomerated dueto fine particles. As a result, it may be difficult to form a uniformgluing agent-coating layer on the surface of the extender pigments, anduniformly adhere the black pigments in the form of a uniform adhesioncoat onto the surface of the gluing agent-coating layer.

[0070] The extender pigments have a BET specific surface area value ofpreferably not less than 15 m²/g, more preferably not less than 20 m²/g,most preferably not less than 25 m²/g. When the BET specific surfacearea value is less than 15 m²/g, the extender pigments may become coarseand the obtained black colorant may also become coarse, so that theink-jet printing ink produced by using such a coarse black colorant maytend to be deteriorated in dispersion stability, and cause clogging of ahead portion of an ink-jet recording apparatus. In the consideration offorming a uniform gluing agent-coating layer on the surface of theextender pigments and uniformly adhering the black pigments in the formof a uniform adhesion coat onto the surface of the gluing agent-coatinglayer, the upper limit of the BET specific surface area value of theextender pigments is preferably 1,000 m²/g, more preferably 750 m²/g,most preferably 500 m²/g.

[0071] The extender pigments as the core particles used in the presentinvention have a specific gravity of preferably 1.3 to 4.2, morepreferably 1.4 to 3.8, still more preferably 1.5 to 3.4. When thespecific gravity of the core particles is more than 4.2, the specificgravity of the obtained black colorant may also become too high.

[0072] As to the hue of the extender pigments as the core particles, theC* value thereof is preferably not more than 12.0, more preferably notmore than 10.0, still more preferably not more than 8.00. When the C*value of the core particles is more than 12.0, it may be difficult toobtain the aimed black colorant exhibiting a high blackness.

[0073] The extender pigments used in the present invention have a hidingpower of preferably less than 200 cm²/g, more preferably not more than150 cm²/g, most preferably not more than 100 cm²/g. When the hidingpower of the extender pigments is not less than 200 cm²/g, it may bedifficult to obtain a black colorant having a high blackness.

[0074] The gluing agent used in the present invention may be of any kindas long as the black pigment can be adhered onto the surface of the coreparticle therethrough. Examples of the preferred gluing agents mayinclude organosilicon compounds such as alkoxysilanes,fluoroalkylsilanes and polysiloxanes; various coupling agents such assilane-based coupling agents, titanate-based coupling agents,aluminate-based coupling agents and zirconate-based coupling agents;oligomer compounds; polymer compounds or the like. These gluing agentsmay be used alone or in the form of a mixture of any two or morethereof. In the consideration of adhesion strength of the black pigmentonto the surface of the core particle through the gluing agent, the morepreferred gluing agents are the organosilicon compounds such asalkoxysilanes, fluoroalkylsilanes and polysiloxanes, and variouscoupling agents such as silane-based coupling agents, titanate-basedcoupling agents, aluminate-based coupling agents and zirconate-basedcoupling agents.

[0075] In particular, in the case where silica particles are used as thecore particles, the gluing agent is preferably composed of organosiliconcompounds or a silane-based coupling agent. Also, in the case where finecarbon black particles are used as the black pigments, the gluing agentis preferably composed of organosilicon compounds.

[0076] As organosilicon compounds used in the present invention, atleast one organosilicon compound selected from the group consisting of(1) organosilane compounds obtained from alkoxysilane compounds; (2)polysiloxanes, or modified polysiloxanes selected from the groupconsisting of (2-A) polysiloxanes modified with at least one compoundselected from the group consisting of polyethers, polyesters and epoxycompounds (hereinafter referred to merely as “modified polysiloxanes”),and (2-B) polysiloxanes whose molecular terminal is modified with atleast one group selected from the group consisting of carboxylic acidgroups, alcohol groups and a hydroxyl group; and (3) fluoroalkylorganosilane compounds obtained from fluoroalkylsilane compounds.

[0077] The organosilane compounds (1) can be produced from alkoxysilanecompounds represented by the formula (I):

R¹ _(a)SiX_(4-a)  (I)

[0078] wherein R¹ is C₆H₅—, (CH₃)₂CHCH₂— or n-C_(b)H_(2b+1)— (wherein bis an integer of 1 to 18); X is CH₃O— or C₂H₅O—; and a is an integer of0 to 3.

[0079] Specific examples of the alkoxysilane compounds may includemethyltriethoxysilane, dimethyldiethoxysilane, phenyltriethyoxysilane,diphenyldiethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane,phenyltrimethoxysilane, diphenyldimethoxysilane,isobutyltrimethoxysilane, decyltrimethoxysilane or the like.

[0080] Among these alkoxysilane compounds, in view of the desorptionpercentage and the adhering strength of the black pigments,methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilaneand isobutyltrimethoxysilane, phenyltriethyoxysilane are preferred, andmethyltriethoxysilane and methyltrimethoxysilane are more preferred.

[0081] As the polysiloxanes (2), there may be used those compoundsrepresented by the formula (II):

[0082] wherein R² is H— or CH₃—, and d is an integer of 15 to 450.

[0083] As the modified polysiloxanes (2-A), there may be used:

[0084] (a1) polysiloxanes modified with polyethers represented by theformula (III):

[0085] wherein R³ is —(—CH₂—)_(h)—; R⁴ is —(—CH₂—)i—CH₃; R⁵ is —OH,—COOH, —CH═CH₂, —CH(CH3)═CH₂ or —(—CH₂—)_(j)—CH₃; R⁶ is—(—CH₂—)_(k)—CH₃; g and h are an integer of 1 to 15; i, j and k are aninteger of 0 to 15; e is an integer of 1 to 50; and f is an integer of 1to 300;

[0086] (a2) polysiloxanes modified with polyesters represented by theformula (IV):

[0087] wherein R⁷, R⁸ and R⁹ are —(—CH2—)_(q)— and may be the same ordifferent; R¹⁰ is —OH, —COOH, —CH═CH₂, —CH(CH₃)═CH₂ or —(—CH₂—)_(r)—CH₃;R¹¹ is —(—CH₂—)_(s)—CH₃; n and q are an integer of 1 to 15; r and s arean integer of 0 to 15; e′ is an integer of 1 to 50; and f′ is an integerof 1 to 300;

[0088] (a3) polysiloxanes modified with epoxy compounds represented bythe formula (V):

[0089] wherein R¹² is —(—CH₂—)v—; v is an integer of 1 to 15; t is aninteger of 1 to 50; and u is an integer of 1 to 300; or a mixturethereof.

[0090] As the terminal-modified polysiloxanes (2-B), there may be usedthose represented by the formula (VI):

[0091] wherein R¹³ and R¹⁴ are —OH, R¹⁶OH or R¹⁷COOH and may be the sameor different; R¹⁵ is —CH₃ or —C₆H₅; R¹⁶ and R¹⁷ are —(—CH₂—)_(y—);wherein y is an integer of 1 to 15; w is an integer of 1 to 200; and xis an integer of 0 to 100.

[0092] In view of the desorption percentage and the adhering effect ofthe black pigment, polysiloxanes having methyl hydrogen siloxane units,the polysiloxanes modified with the polyethers and the polysiloxaneswhose terminals are modified with carboxylic acid groups are preferred.

[0093] The fluoroalkyl organosilane compounds (3) may be produced fromfluoroalkylsilane compounds represented by the formula (VII):

CF₃ (CF₂)_(z)CH₂CH₂ (R¹⁸)_(a′)SiX_(4-a′)  (VII)

[0094] wherein R¹⁸ is CH₃—, C₂H₅—, CH₃O— or C₂H₅O—; X is CH₃O— orC₂H₅O—; and z is an integer of 0 to 15; and a′ is an integer of 0 to 3.

[0095] Specific examples of the fluoroalkylsilane compounds may includetrifluoropropyl trimethoxysilane, tridecafluorooctyl trimethoxysilane,heptadecafluorodecyl trimethoxysilane, heptadecafluorodecylmethyldimethoxysilane, trifluoropropyl ethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyl triethoxysilane, or the like.Among these fluoroalkylsilane compounds, in view of the desorptionpercentage and the adhering strength of the black pigment,trifluoropropyl trimethoxysilane, tridecafluorooctyl trimethoxysilaneand heptadecafluorodecyl trimethoxysilane are preferred, andtrifluoropropyl trimethoxysilane and tridecafluorooctyl trimethoxysilaneare more preferred.

[0096] As the silane-based coupling agents, there may be exemplifiedvinyltrimethoxysilane, vinyltriethoxysilane,

[0097] γ-aminopropyltriethoxysilane,

[0098] γ-glycidoxypropyltrimethoxysilane,

[0099] γ-mercaptopropyltrimethoxysilane,

[0100] γ-methacryloxypropyltrimethoxysilane,

[0101] N-β(aminoethyl) -γ-aminopropyltrimethoxysilane,

[0102] γ-glycidoxypropylmethyldimethoxysilane,

[0103] γ-chloropropyltrimethoxysilane or the like.

[0104] As the titanate-based coupling agents, there may be exemplifiedisopropyltristearoyl titanate,isopropyltris(dioctylpyrophosphate)titanate,isopropyltri(N-aminoethyl-aminoethyl)titanate,tetraoctylbis(ditridecylphosphate)titanate,tetra(2,2-diaryloxymethyl-1-butyl)bis(ditridecyl)phosphate titanate,his(dioctylpyrophosphate)oxyacetate titanate,bis(dioctylpyrophosphate)ethylene titanate or the like.

[0105] As the aluminate-based coupling agents, there may be exemplifiedacetoalkoxyaluminum diisopropilate,aluminumdiisopropoxymonoethylacetoacetate,aluminumtrisethylacetoacetate, aluminumtrisacetylacetonate or the like.

[0106] As the zirconate-based coupling agents, there may be exemplifiedzirconiumtetrakisacetylacetonate, zirconiumdibutoxybisacetylacetonate,zirconiumtetrakisethylacetoacetate,zirconiumtributoxymonoethylacetoacetate,zirconiumtributoxyacetylacetonate or the like.

[0107] It is preferred to use oligomer compounds having a molecularweight of from 300 to less than 10,000. It is preferred to use polymercompounds having a molecular weight of about 10,000 to about 100,000. Inthe consideration of forming a uniform coating layer on the coreparticles, the oligomers or polymer compounds are preferably in a liquidstate, or soluble in water or various solvents.

[0108] The amount of the gluing agent-coating layer is preferably 0.01to 15.0% by weight, more preferably 0.02 to 12.5% by weight, still morepreferably 0.03 to 10.0% by weight (calculated as C) based on the weightof the gluing agent-coated core particles.

[0109] When the amount of the gluing agent-coating layer is less than0.01% by weight, it may be difficult to adhere not less than one part byweight of the black pigment onto 100 parts by weight of the coreparticles. When the amount of the gluing agent-coating layer is morethan 15.0% by weight, since it is possible to adhere 1 to 500 parts byweight of the black pigment onto 100 parts by weight of the coreparticles therethrough, it is unnecessary to form the gluingagent-coating layer in an amount of more than 15.0% by weight.

[0110] As the black pigments, there may be used carbon black particlessuch as furnace black, channel black and acetylene black, and anilineblack particles. In the consideration of good tinting strength of theobtained black colorant, among these black pigments, the carbon blackparticles are preferred.

[0111] Specific examples of the carbon black particles may include#3050, #3150, #3250, #3750, #3950, MA100, MA7, #1000, #2400B, #30, MA77,MA8, #650, MA11, #50, #52, #45, #2200B and MA600 (tradenames; producedby Mitsubishi Kagaku Co., Ltd.); SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H,SEAST 300 and SEAST FM (tradenames; produced by Tokai Carbon Co., Ltd.),Raven 1250, Raven 860, Raven 1000 and Raven 119OULTRA (tradenames;produced by Columbian Chemicals Co.); KETJENBLACK EC and KETJENBLACKEC600JD (tradenames; produced by Ketjen Black International Company);BALCK PEARLS-L, BALCK PEARLS 1000, BALCK PEARLS 4630, VULCAN XC72, REGAL660 and REGAL 400 (tradenames; produced by Cabot Specialty ChemicalsInc.); or the like.

[0112] The amount of the black pigments adhered is preferably 1 to 500parts by weight, more preferably 30 to 400 parts by weight, mostpreferably 50 to 300 parts by weight based on 100 parts by weight of theextender pigments.

[0113] When the amount of the black pigments adhered is less than onepart by weight, the amount of the black pigments coated on the surfaceof the extender pigments is too small, so that it may be difficult toobtain the aimed black colorant having a high blackness. When the amountof the black pigments adhered is more than 500 parts by weight, theblack pigments may tend to be desorbed from the surface of the obtainedblack colorant because of a too large amount of the black pigmentsadhered. As a result, the resultant black colorant may tend to bedeteriorated in dispersibility in ink-jet printing ink.

[0114] The particle shape and particle size of the black colorant forink-jet printing ink according to the present invention may mainlydepend upon those of the extender pigments as core particles.Specifically, the black colorant may have a particle shape similar tothat of the core particles as well as a slightly larger particle sizethan that of the core particles.

[0115] Specifically, the black colorant for ink-jet printing inkaccording to the present invention has an average particle diameter ofusually 0.001 to 0.15 μm, preferably 0.003 to 0.12 μm, more preferably0.005 to 0.10 μm.

[0116] When the average particle diameter of the black colorant is morethan 0.15 μm, it may be difficult to inhibit the ink-jet printing inkobtained by using such a black colorant from clogging a head portion ofan ink-jet recording apparatus, because of a too large particle sizethereof. When the average particle diameter of the black colorant isless than 0.001 μm, the black colorant tends to be agglomerated togetherdue to fine particles, so that it may become difficult to disperse theblack colorant in the ink-jet printing ink.

[0117] The black colorant of the present invention have a BET specificsurface area value of preferably 15 to 1,000 m²/g, more preferably 20 to750 m²/g, most preferably 25 to 500 m²/g. When the BET specific surfacearea value is less than 15 m²/g, the obtained black colorant may becomecoarse, so that it may be difficult to inhibit the ink-jet printing inkobtained using such a black colorant from clogging a heat portion of anink-jet recording apparatus. When the BET specific surface area value ismore than 1,000 m²/g, the obtained black colorant may tend to beagglomerated together due to fine particles, resulting in deteriorateddispersibility in ink-jet printing ink.

[0118] As to the blackness of the black colorant of the presentinvention, the L* value thereof is preferably not more than 22.0, morepreferably not more than 21.0, still more preferably not more than 20.0.When the L* value is more than 22.0, the obtained colorant may tend toexhibit a too high brightness and, therefore, may fail to show anexcellent blackness. The lower limit of the L* value of the blackcolorant is 14.5.

[0119] The black colorant of the present invention has a specificgravity of preferably 1.3 to 3.0, more preferably 1.4 to 2.6, mostpreferably 1.5 to 2.2. When the specific gravity of the black colorantis more than 3.0, the ink-jet printing ink obtained by using such ablack colorant may tend to be deteriorated in dispersion stability.

[0120] The tinting strength of the black colorant for ink-jet printingink according to the present invention is preferably not less than 110%,more preferably not less than 115%, still more preferably not less than120% when measured by the below-mentioned evaluation method.

[0121] The degree of desorption of the black pigments from the blackcolorant for ink-jet printing ink according to the present invention ispreferably the rank 5 or 4, more preferably the rank 5 when visuallyobserved and evaluated by the below-mentioned method. When the degree ofdesorption of the black pigments is the rank 1, 2 or 3, uniformdispersion of the black colorant for ink-jet printing ink in ink-jetprinting inks or vehicles tends to be inhibited by the desorbed blackpigments.

[0122] As to the light resistance of the black colorant for ink-jetprinting ink according to the present invention, the ΔE* value thereofis preferably not more than 3.0, more preferably not more than 2.5,still more preferably not more than 2.0 when measured by thebelow-mentioned evaluation method. When the ΔE* value is more than 3.0,images printed with an ink-jet printing ink using such a black colorantas well as paints and resin compositions using the black colorant mayfail to show a sufficient light resistance.

[0123] At least a part of the surface of the black colorant for ink-jetprinting ink according to the present invention may be further coated,if required, with a surfactant and/or a polymeric dispersing agent. Theblack colorant coated with the surfactant and/or polymeric dispersingagent can be improved in dispersibility in ink-jet printing inks as wellas dispersion stability as compared to the uncoated black colorant.

[0124] Examples of the surfactant may include anionic surfactants,nonionic surfactants and cationic surfactants. In the consideration ofthe effect of improving dispersibility in ink-jet printing inks as wellas dispersion stability, among these surfactants, the anionicsurfactants and nonionic surfactants are preferred.

[0125] Specific examples of the preferred anionic surfactants mayinclude fatty acid salts, sulfuric acid esters, sulfonic acid salts,phosphoric acid esters or the like. Among these anionic surfactants,sulfuric acid esters and sulfonic acid salts are more preferred.

[0126] Specific examples of the preferred nonionic surfactants mayinclude polyethylene glycol-type nonionic surfactants such aspolyoxyethylene alkyl ethers and polyoxyethylene aryl ethers; polyhydricalcohol-type nonionic surfactants such as sorbitan fatty acid esters; orthe like. Among these nonionic surfactants, polyethylene glycol-typenonionic surfactants are more preferred.

[0127] Specific examples of the preferred cationic surfactants mayinclude amine salt-type cationic surfactants, quaternary ammoniumsalt-type cationic surfactants or the like. Among these cationicsurfactants, the quaternary ammonium salt-type cationic surfactants aremore preferred.

[0128] As the polymeric dispersing agent, there may be usedalkali-soluble resins such as styrene-acrylic acid copolymers,styrene-maleic acid copolymers, polyacrylic acid derivatives or thelike.

[0129] The coating amount of the surfactant and/or polymeric dispersingagent is preferably 0.1 to 10.0% by weight, more preferably 0.2 to 7.5%by weight, still more preferably 0.3 to 5.0% by weight (calculated as C)based on the weight of the black colorant coated with the surfactantand/or polymeric dispersing agent.

[0130] When the coating amount of the surfactant and/or polymericdispersing agent is less than 0.1% by weight, it may be difficult toimprove the dispersibility in ink-jet printing inks as well as thedispersion stability. When the coating amount of the surfactant and/orpolymeric dispersing agent is more than 10% by weight, the effect ofimproving the dispersibility in ink-jet printing inks as well as thedispersion stability is already saturated. Therefore, it is unnecessaryand meaningless to coat the black colorant with the surfactant and/orpolymeric dispersing agent in such a large amount.

[0131] The black colorant coated with the surfactant and/or polymericdispersing agent according to the present invention is substantially thesame in particle size, BET specific surface area value, specificgravity, blackness, tinting strength, light resistance and degree ofdesorption of black pigments as those of the black colorant uncoatedwith the surfactant and/or polymeric dispersing agent according to thepresent invention.

[0132] In the black colorant for ink-jet printing ink according to thepresent invention, if required, the surface of the core particle may bepreviously coated with at least one compound selected from the groupconsisting of hydroxides of aluminum, oxides of aluminum, hydroxides ofsilicon and oxides of silicon. The black colorant for ink-jet printingink using the core particles having such a coat composed of at least onecompound selected from the group consisting of hydroxides of aluminum,oxides of aluminum, hydroxides of silicon and oxides of silicon(hereinafter referred to merely as “intermediate coat”), can be moreeffectively reduced in amount of black pigments desorbed from thesurface of the extender pigments as compared to those using the coreparticles having no intermediate coat.

[0133] The amount of the intermediate coat is preferably 0.01 to 20% byweight (calculated as Al, SiO₂ or a sum of Al and SiO₂) based on theweight of the extender pigments as the core particles coated with theintermediate coat.

[0134] When the amount of the intermediate coat is less than 0.01% byweight, it may be difficult to attain the effect of reducing the amountof black pigments desorbed. As long as the amount of the intermediatecoat is in the range of 0.01 to 20% by weight, the effect of reducingthe amount of black pigments desorbed can be sufficiently attained.Therefore, it is unnecessary to form the intermediate coat in an amountof more than 20% by weight.

[0135] The black colorant for ink-jet printing ink produced by using theextender pigments as the core particles having the intermediate coataccording to the present invention are substantially the same inparticle size, BET specific surface area value, specific gravity,blackness, tinting strength and light resistance as those of the blackcolorant using the extender pigments as the core particles having nointermediate coat according to the present invention. The degree ofdesorption of the black pigments from the black colorant can be improvedby forming the intermediate coat on the extender pigments as the coreparticles such that the black colorant can show a black pigmentdesorption degree of preferably the rank 5.

[0136] Next, the ink-jet printing ink containing the black colorant ofthe present invention is described.

[0137] The ink-jet printing ink of the present invention comprises theblack colorant for ink-jet printing ink according to the presentinvention, a dispersant and water, and may further contain, if required,a water-soluble resin, a penetrant, a humectant, a water-solublesolvent, a pH modifier, a preservative or the like.

[0138] The amount of the black colorant contained in the ink-jetprinting ink is usually 1 to 20% by weight based on the weight of theink base solution.

[0139] The amount of the dispersant contained in the ink-jet printingink is preferably 5 to 200% by weight, more preferably 7.5 to 150% byweight, still more preferably 10 to 100% by weight based on the weightof the black colorant for the ink-jet printing ink.

[0140] As the dispersant, there may be used the same surfactants and/orpolymeric dispersing agents as used for coating the surface of the blackcolorant. In the consideration of good dispersibility of the blackcolorant in the ink-jet printing ink and good dispersion stability ofthe obtained ink, as the surfactant, anionic surfactants and nonionicsurfactants are preferred, and as the polymeric dispersing agent,water-soluble resins such as styrene-acrylic acid copolymers arepreferred.

[0141] As the solvent for the ink-jet printing ink, water may be used,if required, in combination with a water-soluble organic solvent. Theamount of the water-soluble organic solvent contained in the ink-jetprinting ink is preferably 1 to 50% by weight, more preferably 1 to 40%by weight, still more preferably 1 to 30% by weight based on the weightof the ink base solution.

[0142] Examples of the water-soluble organic solvent may includemonohydric alcohols such as methanol, ethanol, n-propanol andisopropanol; dihydric alcohols such as ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, propylene glycol anddipropylene glycol; trihydric alcohols such as glycerol; polyalkyleneglycols such as polyethylene glycol; lower alkyl esters of polyhydricalcohols such as diethylene glycol monobutyl ether, ethylene glycolmonobutyl ether and ethylene glycol monoethyl ether; or the like. Thesewater-soluble organic solvents may be used alone or in the from of amixture of any two or more thereof. Among these water-soluble organicsolvents, dihydric alcohols are preferred.

[0143] The black colorant dispersed in the ink-jet printing inkaccording to the present invention has an average dispersed particlediameter (D₅₀) of preferably not more than 0.2 μm, more preferably notmore than 0.15 μm, still more preferably not more than 0.1 μm. When thedispersed particle diameter (D₅₀) of the black colorant contained in theink is more than 0.2 μm, a head portion of the ink-jet recordingapparatus may tend to be clogged therewith, and the dispersibility ofthe black colorant in the ink-jet printing ink may tend to bedeteriorated.

[0144] The dispersion stability of the ink-jet printing ink according tothe present invention is preferably the rank 4 or 5, more preferably therank 5 when visually observed and evaluated by the below-mentionedmethod. The percentage of change in dispersed particle diameter (D₅₀) ispreferably not more than 10%, more preferably not more than 8%.

[0145] As to the blackness of printed images formed by using the ink-jetprinting ink of the present invention, the L* value thereof ispreferably not more than 22.0, more preferably not more than 21.0, mostpreferably not more than 20.0. When the L* value is more than 22.0, theresultant printed images tends to exhibit a too high brightness and,therefore, may fail to exhibit an excellent blackness. The lower limitof the L* value of the printed images is 14.5.

[0146] As to the light resistance of the printed images obtained byusing the ink-jet printing ink of the present invention, the ΔE* valuethereof is preferably not more than 3.0, more preferably not more than2.5, still more preferably not more than 2.0.

[0147] The ink-jet printing ink of the present invention has ananti-clogging property at a head portion of preferably the rank 4 or 5,more preferably the rank 5 when visually observed and evaluated by thebelow-mentioned method.

[0148] Next, the aqueous pigment dispersion containing the blackcolorant for the ink-jet printing ink according to the present inventionwhich dispersion is used for the production of the ink-jet printing ink,is described.

[0149] The aqueous pigment dispersion of the present invention containsthe black colorant for ink-jet printing ink according to the presentinvention in an amount of usually 10 to 40% by weight, preferably 15 to35% by weight.

[0150] The aqueous pigment dispersion of the present invention comprisesthe above black colorant for ink-jet printing ink, a dispersant andwater, and may further contain, if required, a water-soluble resin, awater-soluble solvent or the like.

[0151] As the dispersant for the aqueous pigment dispersion, there maybe used the same dispersants as those used in the above ink-jet printingink.

[0152] The dispersed particle diameter (D₅₀) of the black colorantcontained in the aqueous pigment dispersion of the present invention ispreferably not more than 0.15 μm, more preferably not more than 0.12 μm,still more preferably not more than 0.09 μm.

[0153] The dispersion stability of the aqueous pigment dispersion of thepresent invention is preferably the rank 4 or 5, more preferably therank 5 when visually observed and evaluated by the below-mentionedmethod. The percentage of change in the dispersed particle diameter(D₅₀) is preferably not more than 12%, more preferably not more than10%.

[0154] The ink-jet printing ink obtained by using the aqueous pigmentdispersion of the present invention can exhibit a more excellentdispersion condition such that the dispersed particle diameter (D₅₀) ofthe black colorant contained in the ink is preferably not more than 0.15μm, more preferably not more than 0.12 μm, still more preferably notmore than 0.09 μm.

[0155] Next, the process for producing the black colorant for ink-jetprinting ink according to the present invention, is described.

[0156] The black colorant for ink-jet printing ink according to thepresent invention can be produced by mixing the extender pigments as thecore particles with the gluing agent to form a gluing agent-coatinglayer on at least a part of the surface of the respective extenderpigments; and then mixing the extender pigments coated with the gluingagent with the black pigments to form a black pigment coat on at least apart of the gluing agent-coating layer.

[0157] The formation of the gluing agent-coating layer on the surface ofthe extender pigments as the core particles may be performed bymechanically mixing and stirring the extender pigments as the coreparticles with the gluing agent, or by mechanically mixing and stirringthe extender pigments as the core particles and the gluing agent whilespraying the gluing agent onto the extender pigments. A substantiallywhole amount of the gluing agent added can be used for coating thesurface of the extender pigments as the core particles.

[0158] Meanwhile, in the case where alkoxysilanes or fluoroalkylsilanesare used as the gluing agent, a part of the alkoxysilanes orfluoroalkylsilanes may be coated in the form of organosilane compoundsproduced from the alkoxysilanes or fluoroalkyl organosilane compoundsproduced form fluoroalkylsilanes through the coating step. Even in sucha case, subsequent adhesion of the black pigment on the gluingagent-coating layer is not adversely affected.

[0159] In order to uniformly coat the gluing agent over the surface ofthe extender pigments as the core particles, it is preferred that theagglomerated extender pigments are previously deaggregated using acrusher.

[0160] The mixing and stirring of the extender pigments as the coreparticles with the gluing agent, the mixing and stirring of the blackpigment with the gluing agent-coated extender pigments, the mixing andstirring of the gluing agent with the extender pigments as the coreparticles coated with the black pigment coat through the gluing agent,and the mixing and stirring of the black pigment and the extenderpigments having the colored adhesion layer and the gluing agent-coatinglayer formed thereon, is preferably carried out using an apparatuscapable of applying a shear force to the powder mixture, especially suchan apparatus capable of simultaneously effecting shear action, spatulastroking and compression. Examples of such apparatuses may includewheel-type kneaders, ball-type kneaders, blade-type kneaders, roll-typekneaders or the like. Among these apparatuses, the wheel-type kneadersare preferred to effectively practice the present invention.

[0161] Specific examples of the wheel-type kneaders may include edgerunners (similar in meaning to mix muller, Simpson mill and sand mill),multi mill, Stotz mill, Wet pan mill, corner mill, ring muller or thelike. Among these kneaders, preferred are edge runners, multi mill,Stotz mill, Wet pan mill and ring muller, and more preferred are edgerunners. Specific examples of the ball-type kneaders may includevibration mill or the like. Specific examples of the blade-type kneadersmay include Henschel mixer, planetary mixer, Nauter mixer or the like.Specific examples of the roll-type kneaders may include extruders or thelike.

[0162] The conditions of the mixing and stirring treatment may beselected so as to uniformly coat the surface of the particle with thegluing agent. Specifically, the mixing and stirring conditions may beappropriately controlled such that the linear load is usually 19.6 to1,960 N/cm (2 to 200 Kg/cm), preferably 98 to 1,470 N/cm (10 to 150Kg/cm), more preferably 147 to 980 N/cm (15 to 100 Kg/cm); the treatingtime is usually 5 minutes to 24 hours, preferably 10 minutes to 20hours; and the stirring speed is usually 2 to 2,000 rpm, preferably 5 to1,000 rpm, more preferably 10 to 800 rpm.

[0163] The amount of the gluing agent added is preferably 0.15 to 45parts by weight based on 100 parts by weight of the extender pigments asthe core particles. When the gluing agent is added in an amount of 0.15to 45 parts by weight, it is possible to adhere 1 to 500 parts by weightof the black pigment onto 100 parts by weight of the extender pigmentsas the core particles.

[0164] After the surface of the core particle is coated with the gluingagent, the black pigment is added, and then mixed and stirred with thecoated core to adhere the black pigment onto the gluing agent-coatinglayer. The obtained particles may be further subjected to drying orheating treatments, if required.

[0165] As the adding method of the black pigments, a continuous additionmethod and a divided addition method may be exemplified. In case ofcontinuously adding the black pigments, the black pigment may be addedslowly and little by little, especially for a period of 5 minutes to 24hours, preferably 5 minutes to 20 hours. In case of dividedly adding theblack pigments, the adding step of the black pigments of 5 to 25 partsby weight based on 100 parts by weight of the extender pigments as thecore particles, and mixing and stirring step under the followingconditions can be repeated until the added amount of the black pigmentsreaches a predetermined amount thereof.

[0166] The mixing and stirring conditions may be appropriately selectedso as to form a uniform black pigment coat on the gluing agent-coatinglayer, and may be controlled such that the linear load is usually 19.6to 1,960 N/cm (2 to 200 Kg/cm), preferably 98 to 1,470 N/cm (10 to 150Kg/cm), more preferably 147 to 980 N/cm (15 to 100 Kg/cm); the treatingtime is usually 5 minutes to 24 hours, preferably 10 minutes to 20hours; and the stirring speed is usually 2 to 2,000 rpm, preferably 5 to1,000 rpm, more preferably 10 to 800 rpm.

[0167] The amount of the black pigments added is usually 1 to 500 partsby weight, preferably 30 to 400 parts by weight, more preferably 50 to300 parts by weight based on 100 parts by weight of the extenderpigments as the core particles. When the amount of the black pigmentsadded is out of the above-specified range, it may be difficult to obtainthe aimed black colorant for ink-jet printing ink.

[0168] The heating temperature used in the drying and heating treatmentsis preferably 40 to 150° C., more preferably 60 to 120° C., and theheating time is preferably 10 minutes to 12 hours, more preferably 30minutes to 3 hours.

[0169] Meanwhile, in the case where alkoxysilanes or fluoroalkylsilanesare used as the gluing agent, a coating layer composed of organosilanecompounds obtainable from the alkoxysilanes or fluorine-containingorganosilane compounds obtainable from the fluoroalkylsilanes is finallyformed on the surface of the extender pigments as the core particleswhen treated through these steps.

[0170] In the production of the black colorant for ink-jet printing inkaccording to the present invention, the black pigments added are finelydivided and adhered in the form of a uniform adhesion coat on thesurface of the extender pigments via the gluing agent-coating layer whentreated through the above steps.

[0171] The black colorant for ink-jet printing ink whose surface iscoated with the surfactant and/or polymeric dispersing agent accordingto the present invention can be produced by coating the above-obtainedblack colorant with the surfactant and/or polymeric dispersing agent.

[0172] The formation of the surfactant and/or polymeric dispersing agentcoating layer on the surface of the black colorant may be performed bymechanically mixing and stirring the black colorant with the surfactantand/or polymeric dispersing agent.

[0173] The amount of the surfactant and/or polymeric dispersing agentadded is preferably 0.05 to 50 parts by weight based on 100 parts byweight of the black colorant. By adding the surfactant and/or polymericdispersing agent in an amount of 0.05 to 50 parts by weight, it ispossible to further improve a dispersibility of the black colorant inink-jet printing ink, and a dispersion stability of the obtained ink.

[0174] The core particles may be previously coated, if required, with atleast one compound selected from the group consisting of hydroxides ofaluminum, oxides of aluminum, hydroxides of silicon and oxides ofsilicon, prior to mixing and stirring with the gluing agent.

[0175] The formation of the intermediate coat is conducted as follows.That is, an aluminum compound, a silicon compound or both the aluminumand silicon compounds are added to a water suspension prepared bydispersing the core particles in water. The resultant mixture is mixedand stirred together and then, if required, the pH value thereof isadjusted adequately, thereby forming the intermediate coat, on thesurface of the core particle. Thereafter, the thus-obtained coreparticles coated with at least one compound selected from the groupconsisting of hydroxides of aluminum, oxides of aluminum, hydroxides ofsilicon and oxides of silicon are filtered out, washed with water, driedand then pulverized, and may be further subjected to subsequenttreatments such as deaeration and compaction, if required.

[0176] Examples of the aluminum compound may include aluminum salts suchas aluminum acetate, aluminum sulfate, aluminum chloride and aluminumnitrate, alkali aluminates such as sodium aluminate, or the like.

[0177] Examples of the silicon compound may include water glass #3,sodium orthosilicate, sodium metasilicate or the like.

[0178] Next, the process for producing the ink-jet printing inkaccording to the present invention, is described.

[0179] The ink-jet printing ink according to the present invention canbe produced by mixing and dispersing a necessary amount of the blackcolorant for ink-jet printing ink according to the present invention, adispersant and water, if required, together with various additives suchas a penetrant, a humectant, a water-soluble solvent, a pH modifier anda preservative using a dispersing device to form a primary dispersion;further mixing and dispersing the obtained dispersion together withwater, a water-soluble solvent and other additives; and then filteringthe resultant dispersion using a membrane filter.

[0180] As the dispersing device, there may be used a ball mill, a sandmill, an attritor, a roll mill, a beads mill, a colloid mill, anultrasonic homogenizer, a high-pressure homogenizer or the like.

[0181] Next, the process for producing the aqueous pigment dispersionaccording to the present invention is described.

[0182] The aqueous pigment dispersion according to the present inventioncan be produced by mixing and dispersing a necessary amount of the blackcolorant, a dispersant and water, if required, together with variousadditives such as a water-soluble resin and a water-soluble solventusing a dispersing device; and then filtering the resultant dispersionusing a membrane filter.

[0183] As the dispersing device, there may be used a disper, a ballmill, a sand mill, an attritor, a roll mill, a beads mill, a colloidmill, an ultrasonic homogenizer, a high-pressure homogenizer or thelike.

[0184] When the aqueous pigment dispersion of the present invention isused for the production of the ink-jet printing ink, a necessary amountof the aqueous pigment dispersion, a dispersant and water are mixed anddispersed, if required, together with various additives such as awater-soluble resin, a penetrant, a humectant, a water-soluble solvent,a pH modifier and a preservative using a dispersing device, and theresultant dispersion is filtered using a membrane filter to produce theink-jet printing ink.

[0185] The aqueous pigment dispersion of the present invention may beused in such an amount that the concentration of pigments contained inthe obtained ink-jet printing ink is in the range of 1 to 20% by weight.

[0186] As the dispersing device, there may be used the same dispersingdevices as described above.

[0187] The point of the present invention is that the black colorant forink-jet printing ink comprising the extender pigments as the coreparticles, the gluing agent-coating layer formed on at least a part ofthe surface of the extender pigments as the core particle and the blackpigments adhered in the form of a uniform adhesion coat onto at least apart of the gluing agent-coating layer, can exhibit not only a hightinting strength and a high blackness, but also excellent dispersibilityand light resistance in spite of fine particles.

[0188] The reason why the black colorant for ink-jet printing inkaccording to the present invention can exhibit a high blackness, isconsidered as follows. That is, since the extender pigments as the coreparticles have a low chroma and a low hiding power, the black pigmentscan exhibit an inherent hue thereof without being hidden and interferedby the hue of the core particles.

[0189] The reason why the black colorant for ink-jet printing inkaccording to the present invention can exhibit an excellentdispersibility, is considered as follows. That is, since the extenderpigments as the core particles used have a relatively highdispersibility and the black pigments are strongly adhered onto thesurface of the core particles through the gluing agent, the amount ofthe black pigments desorbed from the black colorant, so that the blackcolorant is well dispersed in the system without disturbance by thedesorbed black pigments.

[0190] Also, when the surface of the black colorant for ink-jet printingink is coated with the surfactant and/or polymeric dispersing agent, theink-jet printing ink using such a coated black colorant can exhibit amore excellent dispersion stability. The reason therefor is consideredto be that by coating the surface of the black colorant of the presentinvention with the surfactant and/or polymeric dispersing agent capableof acting as a hydrophilic surface modifier, the black colorant can beuniformly and stably dispersed in the ink-jet printing ink almostconstituted of water.

[0191] The ink-jet printing ink of the present invention can exhibit notonly an excellent dispersion stability, but also is free from cloggingat a head portion of an ink-jet recording apparatus. In addition,printed images formed by using the ink-jet printing ink can exhibit ahigh blackness and an excellent light resistance.

[0192] The reason why the ink-jet printing ink of the present inventioncan exhibit an excellent dispersion stability, is considered as follow.That is, in general, the black pigments are present in the ink basesolution in the form of dispersed particles having a dispersed particlediameter (D₅₀) of about 0.2 μm and, therefore, tend to beself-agglomerated and precipitated with the passage of time. On thecontrary, in the case of the black colorant for ink-jet printing inkaccording to the present invention, since the black pigments are adheredin the form of a uniform adhesion coat onto the surface of the extenderpigments ordinarily used as an anti-precipitating agent, the individualblack colorant particles can exist in the ink base solution in awell-dispersed condition.

[0193] The reason why the ink-jet printing ink of the present inventionis free from clogging at a head portion of an ink-jet recordingapparatus, is considered as follows. That is, in general, black pigmentsare difficult to finely disperse in the ink base solution. In addition,since the black pigments are ordinary present in the ink base solutionin the form of dispersed particles having a dispersed particle diameter(D₅₀) of about 0.2 μm, the black pigments tend to be self-agglomeratedwith the passage of time. As a result, the particle size of theagglomerated black pigments becomes larger than a nozzle diameter of thehead portion of the ink-jet recording apparatus, thereby causingclogging of the head portion. On the contrary, in the case of the blackcolorant for ink-jet printing ink according to the present invention,since the black pigments are adhered onto the surface of the extenderpigments in the form of a uniform adhesion coat, the black colorant forink-jet printing ink according to the present invention can be presentin the ink base solution in a well-dispersed condition withoutself-agglomeration thereof.

[0194] The reason why the printed images obtained using the ink-jetprinting ink of the present invention can exhibit a high blackness, isconsidered as follows. That is, in the case of the black colorant forink-jet printing ink according to the present invention, the blackpigments which are usually present in the ink base solution in the formof dispersed particles having a dispersed particle diameter (D₅₀) ofabout 0.2 μm, are adhered onto the surface of the extender pigments inthe form of a uniform adhesion coat, namely the individual blackpigments can be kept in such a state similar to particles extremelyfinely dispersed in the ink. In addition, the black colorant itself canexhibit an excellent dispersibility in the ink.

[0195] The reason why the printed images obtained using the ink-jetprinting ink of the present invention can exhibit an excellent lightresistance, is considered as follows. The black colorant of the presentinvention, which are obtained by adhering the black pigments having aremarkably excellent light resistance in the form of a uniform adhesioncoat as compared to dyes onto the surface of the extender pigments, isused as a black colorant for the ink-jet printing ink.

[0196] The black colorant for ink-jet printing ink according to thepresent invention can exhibit not only a high tinting strength and ahigh blackness, but also excellent dispersibility and light resistancein spite of fine particles and, therefore, can be suitably used as ablack colorant for ink-jet printing ink.

[0197] The ink-jet printing ink of the present invention can exhibit anexcellent dispersion stability, and can be prevented from clogging ahead portion of an ink-jet recording apparatus. In addition, the printedimages obtained using the ink-jet printing ink of the present inventioncan exhibit a high blackness and an excellent light resistance.Therefore, the ink-jet printing ink of the present invention can besuitably used as an ink for ink-jet recording.

EXAMPLES

[0198] The present invention is described in more detail by Examples andComparative Examples, but the Examples are only illustrative and,therefore, not intended to limit the scope of the present invention.

[0199] Various properties were evaluated by the following methods.

[0200] (1) The average particle size of the particles was expressed byan average value of 350 particles observed on a micrograph (×50,000).

[0201] (2) The sphericity was expressed by a ratio of average particlediameter (average maximum diameter) to average minimum diameter.

[0202] (3) The specific surface area was expressed by the value measuredby a BET method.

[0203] (4) The specific gravity of each of the extender pigments, blackpigments, black colorant was measured using a “Multi-Volume Densitometer1305-Model” (manufactured by Micro-Meritix Co., Ltd.).

[0204] (5) The amounts of Al and Si present on the surface of theextender pigments coated with the intermediate coating layer, and theamount of Mn contained in Mn-containing hematite particles as thebelow-mentioned core particles 6 were measured by a fluorescent X-rayanalyzer “3036M-Model” (manufactured by RIGAKU DENKI KOGYO CO., LTD.)according to “General Rule for Fluorescent X-ray Analysis” prescribed inJIS K0119.

[0205] (6) The amount of the gluing agent-coating layer formed on thesurface of the extender pigments, the amount of the black pigmentsadhered to the black colorant, and the amount of the surfactant and/orpolymeric dispersing agent coated on the surface of the black colorant,were respectively determined by measuring the carbon contents using“Horiba Metal, Carbon and Sulfur Analyzer EMIA-2200 Model” (manufacturedby Horiba Seisakusho Co., Ltd.).

[0206] (7) The degree of desorption of the black pigments from the coreparticles was visually observed and evaluated by the following method,and the observation results were classified into the following fiveranks. The rank 5 represents that the amount of the black pigmentsdesorbed from the surface of the extender pigments was smallest.

[0207] That is, 2 g of the particles to be measured and 20 ml of ethanolwere placed in a 50-ml conical flask and then was subjected toultrasonic dispersion for 60 minutes. Thereafter, the obtaineddispersion was centrifuged at a rotating speed of 10,000 rpm for 15minutes to separate the particles from the solvent. The obtainedparticles were dried at 80° C. for one hour, and the micrograph(×50,000) thereof was visually observed to count the number of thedesorbed and re-aggregated black pigment particles present in visualfield of the micrograph. The micrograph was compared with a micrograph(×50,000) of mixed particles obtained by simply mixing the coreparticles with the black pigments without forming the gluingagent-coating layer. The results are classified into the following fiveranks.

[0208] Rank 1; Number of desorbed and re-aggregated particles wassubstantially the same as that in the simply mixed particles;

[0209] Rank 2; 30 to 49 desorbed and re-aggregated particles per 100core particles were recognized;

[0210] Rank 3; 10 to 29 desorbed and re-aggregated particles per 100core particles were recognized;

[0211] Rank 4; 5 to 9 desorbed and re-aggregated particles per 100 coreparticles were recognized;

[0212] Rank 5; 0 to 4 desorbed and re-aggregated particles per 100 coreparticles were recognized.

[0213] (8) The hue of the extender pigments and the blackness of each ofthe black pigments and the black colorant, were measured by thefollowing method.

[0214] That is, 0.5 g of each sample and 0.5 ml of castor oil wereintimately kneaded together by a Hoover's muller to form a paste. 4.5 gof clear lacquer was added to the obtained paste and was intimatelykneaded to form a paint. The obtained paint was applied on a cast-coatedpaper by using a 150 μm (6-mil) applicator to produce a coating filmpiece (having a film thickness of about 30 μm). The thus obtainedcoating film piece was measured by a Multi-Spectro-Colour-Meter“MSC-IS-2D” (manufactured by SUGA SHIKENKI CO., LTD.) to determine colorspecification values (L*, a* and b* values) according to JIS Z 8729. Thehue of the extender pigments was expressed by the L*, a* and b* valuesand the blackness of each of the black pigments and the black colorantwas expressed by the L* value. Here, the L* value represents abrightness, and the smaller the L* value, the more excellent theblackness. Meanwhile, the C* value representing chroma is calculatedaccording to the following formula:

C* =( (a*)²+(b*)²)^(½)

[0215] (9) The tinting strength of each of the black colorant wasmeasured by the following method.

[0216] That is, a primary color enamel and a vehicle enamel prepared bythe below-mentioned method were respectively applied on a cast-coatedpaper by using a 150 μm (6-mil) applicator to produce coating filmpieces. The thus obtained coating film pieces were measured by aMulti-Spectro-Colour-Meter “MSC-IS-2D” (manufactured by SUGA SHIKENKICO., LTD.) to determine a color specification value (L* value) thereofaccording to JIS Z 8729. The difference between the obtained L* valueswas represented by a ΔL* value.

[0217] Next, as a standard sample for the black colorant, a mixedpigment was prepared by simply mixing the black pigments and theextender pigments at the same mixing ratio as used for the production ofthe black colorant for ink-jet printing ink. Using the thus preparedmixed pigment as standard sample, the same procedure as defined abovewas conducted to prepare an primary color enamel and a vehicle enamel,to form coating film pieces and to measure L* values thereof. Thedifference between the L* values was represented by a ΔLs* value.

[0218] From the obtained ΔL* value of the black colorant for ink-jetprinting ink and ΔLs* value of the standard sample, the tinting strength(%) was calculated according to the following formula:

Tinting strength (%)=100+{(ΔLs* −ΔL*)×10}

Preparation of Primary Color Enamel

[0219] 10 g of the above sample particles, 16 g of an amino alkyd resinand 6 g of a thinner were blended together. The resultant mixture wasadded together with 90 g of 3 mm glass beads into a 140-ml glass bottle,and then mixed and dispersed for 45 minutes by a paint shaker. Theobtained mixture was mixed with 50 g of an amino alkyd resin, andfurther dispersed for 5 minutes by a paint shaker, thereby obtaining anprimary color enamel.

Preparation of Vehicle Enamel

[0220] 12 g of the above-prepared primary color enamel and 40 g ofAramic White (titanium dioxide-dispersed amino alkyd resin) were blendedtogether, and the resultant mixture was mixed and dispersed for 15minutes by a paint shaker, thereby preparing a vehicle enamel.

[0221] (10) The hiding power of each of the extender pigments and blackpigments was measured by the cryptometer method according to JISK5101-8.2 using the above-prepared primary color enamel.

[0222] (11) The light resistance of each of the black colorant forink-jet printing ink was measured by the following method.

[0223] That is, the primary color enamel as prepared above was appliedonto a cold-rolled steel plate (0.8 mm×70 mm×150 mm; JIS G-3141) anddried to form a coating film having a thickness of 150 μm. One half ofthe thus prepared test specimen was covered with a metal foil, and anultraviolet light was continuously irradiated over the test specimen atan intensity of 100 mW/cm² for 6 hours using “EYE SUPER UV TESTERSUV-W13” (manufactured by IWASAKI DENKI CO., LTD.). Then, the hues (L*,a* and b* values) of the UV-irradiated portion and the metalfoil-covered non-irradiated portion of the test specimen wererespectively measured using a Multi-Spectro-Colour-Meter “MSC-IS-2D”(manufactured by SUGA SHIKENKI CO., LTD.). The ΔE* value was calculatedfrom differences between the measured hue values of the metalfoil-covered non-irradiated portion and the UV-irradiated portionaccording to the following formula:

ΔE*=[(ΔL*)²+(Δa*)²+(Δb*)²]^(½)

[0224] wherein ΔL* represents the difference between L* values of thenon-irradiated and UV-irradiated portions; Δa* represents the differencebetween a* values of the non-irradiated and UV-irradiated portions; andΔb* represents the difference between b* values of the non-irradiatedand UV-irradiated portions.

[0225] (12) The dispersed particle diameter (D₅₀) of particles containedin the ink-jet printing ink and aqueous pigment dispersion was measuredby a laser diffraction-type particle size distribution measuring device“Model HELOSLA/KA” (manufactured by SYMPATEC Co., Ltd.).

[0226] (13) The dispersion stability of each of the ink-jet printing inkand the aqueous pigment dispersion was evaluated as follows. That is, 25ml of an ink-jet printing ink or aqueous pigment dispersion to bemeasured was placed in a tube color comparison and allowed to stand at60° C. for one month. Then, the degree of precipitation of the blackcolorant contained in the ink-jet printing ink or aqueous pigmentdispersion was visually observed and evaluated. The observation resultswere classified into the following five ranks.

[0227] Rank 1: Length of uncolored portion was not less than 10 cm;

[0228] Rank 2: Length of uncolored portion was from 5 cm to less than 10cm;

[0229] Rank 3: Length of uncolored portion was from 1 cm to less than 5cm;

[0230] Rank 4: Length of uncolored portion was less than 1 cm;

[0231] Rank 5: Uncolored portion was not recognized.

[0232] (14) The percentage of change in dispersed particle diameter(D₅₀) of particles contained in each of the ink-jet printing ink andaqueous pigment dispersion was determined as follows. That is, after anink or aqueous pigment dispersion to be measured was allowed to stand at60° C. for one month, the dispersed particle diameter (D₅₀) of particlescontained therein was measured by a laser diffraction-type particle sizedistribution measuring device “Model HELOSLA/KA” (manufactured bySYMPATEC Co., Ltd.). The percentage of change in dispersed particlediameter (D₅₀) was expressed by the value (%) obtained by dividing theamount of change in dispersed particle diameter (D₅₀) between before andafter the standing test by the dispersed particle diameter (D50)measured before the standing test.

[0233] (15) The blackness of the ink-jet printing ink were expressed bythe color specification value (L* value) according to JIS Z 8729 bymeasuring the hue of images printed on a plain paper “KB” (produced byKOKUYO CO., LTD.) using a Multi-Spectro-Colour-Meter “MSC-IS-2D”(manufactured by SUGA SHIKENKI CO., LTD.).

[0234] (16) The light resistance of the ink-jet printing ink wasmeasured by the following method.

[0235] That is, images were printed on a plain paper “KB” (produced byKOKUYO CO., LTD.) using an ink-jet printing ink to be measured. One halfof the thus printed paper was covered with a metal foil, and anultraviolet light was continuously irradiated over the paper at anintensity of 100 mW/cm² for 6 hours using “EYE SUPER UV TESTER SUV-W13”(manufactured by IWASAKI DENKI CO., LTD.). Then, the hues (L*, a* and b*values) of the printed images on the UV-irradiated portion and the metalfoil-covered non-irradiated portion of the paper were respectivelymeasured using a Multi-Spectro-Colour-Meter “MSC-IS-2D” (manufactured bySUGA SHIKENKI CO., LTD.). The ΔE* value was calculated from differencesbetween the measured hue values of the printed images formed on themetal foil-covered non-irradiated portion and UV-irradiated portion ofthe paper according to the above formula. The light resistance of theink-jet printing ink was expressed by the ΔE* value.

[0236] (17) The anti-clogging property of the ink-jet printing ink wasdetermined as follows. That is, an ink to be measured was filled in anink cartridge of an ink jet printer “DESKJET 970Cxi” (manufactured byHEWLETT PACKARD CORP.) to repeatedly print ink images on plain papers“KB” (produced by KOKUYO CO., LTD.) at room temperature. The printedimages were visually observed to examine the degrees of non-uniformity,lack and non-jetted defects thereof. The observation results wereclassified into the following five ranks.

[0237] Rank 1: Non-uniformity, lack or non-jetted defects of printedimages were caused subsequent to the first printed paper;

[0238] Rank 2: Non-uniformity, lack or non-jetted defects of printedimages were not caused until the 5th printed paper;

[0239] Rank 3: Non-uniformity, lack or non-jetted defects of printedimages were not caused until the 10th printed paper;

[0240] Rank 4: Non-uniformity, lack or non-jetted defects of printedimages were not caused until the 20th printed paper;

[0241] Rank 5: Non-uniformity, lack or non-jetted defects of printedimages were not caused until the 25th printed paper.

Example 1 Production of Black Colorant

[0242] 350 g of methyl hydrogen polysiloxane (tradename: “TSF484”,produced by GE TOSHIBA SILICONE CO., LTD.) was added to 7 kg of silicaparticles as shown in the micrograph (×50,000) of FIG. 1 (particleshape: spherical shape; average particle diameter: 0.022 μm; sphericity:1.06; BET specific surface area value: 193.8 m²/g; specific gravity:2.32; L* value: 92.4; a* value: 0.2; b* value: 0.4; C* value: 0.4;hiding power: 10 cm²/g) while operating an edge runner, and theresultant mixture was mixed and stirred for 45 minutes under a linearload of 588 N/cm (60 Kg/cm) at a stirring speed of 22 rpm.

[0243] Then, 7.0 kg of black pigments as shown in the micrograph(×50,000) of FIG. 2 (kind: carbon black (furnace black); particle shape:granular shape; average particle diameter: 0.022 μm; BET specificsurface area value: 133.5 m²/g; specific gravity: 1.84; L* value: 14.6)were added to the above-obtained mixture for 30 minutes while operatingthe edge runner, and the resultant mixture was mixed and stirred for 120minutes under a linear load of 588 N/cm (60 Kg/cm) at a stirring speedof 22 rpm, thereby adhering the carbon black onto the methyl hydrogenpolysiloxane coating layer formed on the respective silica particles.The obtained particles were dried at 80° C. for 60 minutes using adryer, thereby obtaining a black colorant.

[0244] The thus obtained black colorant was in the form of sphericalparticles having an average particle diameter of 0.026 μm and asphericity of 1.06, and had a BET specific surface area value of 125.4m²/g; a specific gravity of 2.05; a blackness (L* value) of 16.5; atinting strength of 137%; a light resistance (ΔE* value) of 1.1; and ablack pigment desorption degree of Rank 5; and a coating amount ofmethyl hydrogen polysiloxane of 1.34% by weight (calculated as C).Further, it was confirmed that the amount of the carbon black adheredwas 48.70% by weight (calculated as C; corresponding to 100 parts byweight based on 100 parts by weight of the silica particles).

[0245] As a result of observing the micrograph (×50,000) of the obtainedblack colorant as shown in FIG. 3, since almost no black pigments wererecognized from the micrograph, it was confirmed that a substantiallywhole amount of the black pigments used contributed to the formation ofthe black pigment coat on the coating layer composed of methyl hydrogenpolysiloxane. Further, it was recognized that the black pigments adheredno longer maintained the particle shape and size of those initiallyadded, more specifically, the black pigments had a much finer particlesize than that of the core particles and were adhered onto the surfaceof the extender pigments in the form of a uniform adhesion coat.

[0246] On the other hand, the extender pigments and the black pigmentswere simply mixed with each other by the same method as defined aboveexcept that no gluing agent was used. The micrograph (×50,000) of thethus obtained simply mixed particles is shown in FIG. 4. As is apparentfrom the micrograph of FIG. 4, in the case where the black pigments andthe silica particles were simply mixed with each other without using thegluing agent, it was confirmed that the black pigments were not reducedin particle size, and both the particles were dispersed separately andindependently from each other, thereby failing to form a uniform anddense black pigment coat adhered onto the surface of the extenderpigments.

Example 2 Production of Ink-jet Printing Ink I

[0247] 88.5 parts by weight of ion-exchanged water and 1.2 parts byweight of a dispersant (mixture of polyacrylic acid and styrene-maleicacid copolymer (mixing ratio: 8:2)) were charged into a sand mill andmixed with each other. Then, 10.0 parts by weight of the black colorantobtained in Example 1 and 0.3 part by weight of a defoaming agent(silicone-based defoamer) were added to the mixed solution, and theresultant mixture was mixed and dispersed for one hour, therebyobtaining a primary dispersion for an ink-jet printing ink.

[0248] Next, the following components were mixed and stirred at themixing ratio shown below, and the resultant mixture was passed through a0.5 μm-mesh membrane filter, thereby obtaining an ink-jet printing ink.

Ink Composition

[0249] Primary dispersion for ink-jet printing ink 10.0 parts by weightDiethylene glycol 2.0 parts by weight Ion-exchanged water 8.0 parts byweight

[0250] The thus obtained ink-jet printing ink had a dispersed particlediameter (D₅₀) of 0.03 μm; a dispersion stability (by visualobservation) of Rank 5; a percentage of change in dispersed particlediameter of 6.4%; a blackness (L* value) of 17.8; a light resistance(ΔE* value) of 1.8; and an anti-clogging property of Rank 5.

Example 3 Production of Aqueous Pigment Dispersion

[0251] 78.5 parts by weight of ion-exchanged water and 1.2 parts byweight of a dispersant (mixture of polyacrylic acid and styrene-maleicacid copolymer (mixing ratio: 8:2)) were charged into a sand mill andmixed with each other. Then, 20.0 parts by weight of the black colorantobtained in Example 1 and 0.3 part by weight of a defoaming agent(silicone-based defoamer) were added to the mixed solution, and theresultant mixture was mixed and dispersed for one hour and passedthrough a 0.5 μm-mesh membrane filter, thereby obtaining an aqueouspigment dispersion.

[0252] The thus obtained aqueous pigment dispersion had a dispersedparticle diameter (D₅₀) of 0.04 μm; a dispersion stability (by visualobservation) of Rank 5; and a percentage of change in dispersed particlediameter (D₅₀) of 7.9%.

Example 4 Production of Ink-jet Printing Ink II

[0253] 25.0 parts by weight of the aqueous pigment dispersion obtainedin Example 3, 64.6 parts by weight of ion-exchanged water, 10.0 parts byweight of diethylene glycol, 0.3 part by weight of a dispersant (mixtureof polyacrylic acid and styrene-maleic acid copolymer (mixing ratio:8:2)) and 0.1 part by weight of a defoaming agent (silicone-baseddefoamer) were charged into a sand mill, mixed and dispersed for onehour and then passed through a 0.5 μm-mesh membrane filter, therebyobtaining an ink-jet printing ink II.

[0254] The thus obtained ink-jet printing ink had a dispersed particlediameter (D₅₀) of 0.02 μm; a dispersion stability (by visualobservation) of Rank 5; a percentage of change in dispersed particlediameter (D₅₀) of 5.8%; a blackness (L* value) of 17.7; a lightresistance (ΔE* value) of 1.7; and an anti-clogging property of Rank 5.

Core Particles 1 to 7

[0255] Core particles 1 to 7 having properties shown in Table 1 wereprepared.

Core particles 8

[0256] A slurry containing silica particles was obtained by dispersing20 kg of silica particles (core particles 1) in 150 liters of water. ThepH value of the thus obtained slurry containing the silica particles wasadjusted to 10.5, and then the slurry concentration was adjusted to 98g/liter by adding water thereto. After 150 liters of the slurry washeated to 60° C., 2,722 ml of a 1.0 mol/liter NaAlO₂ solution(corresponding to 0.5% by weight (calculated as Al) based on the weightof the silica particles) was added to the slurry. After allowing theobtained slurry to stand for 30 minutes, the pH value of the slurry wasadjusted to 7.5 by using acetic acid. After further allowing theresultant slurry to stand for 30 minutes, the slurry was subjected tofiltration, washing with water, drying and pulverization, therebyobtaining the silica particles whose surface was coated with hydroxidesof aluminum.

[0257] Various properties of the obtained silica particles coated withthe hydroxides of aluminum are shown in Table 3.

Core Particles 9 to 13

[0258] The same procedure as defined for the production of the abovecore particles 8, was conducted except that kinds of core particles, andkinds and amounts of additives added in the surface-treating step werechanged variously, thereby obtaining surface-treated core particles.

[0259] The essential treatment conditions are shown in Table 2, andvarious properties of the obtained surface-treated core particles areshown in Table 3.

[0260] Meanwhile, in Tables, “A” and “S” as described in “kind ofcoating material used in surface-treating step” represent hydroxides ofaluminum and oxides of silicon, respectively.

Black Pigments A to C

[0261] Black pigments A to C having properties as shown in Table 4 wereprepared.

Examples 5 to 17 and Comparative Examples 1 to 5

[0262] The same procedure as defined in Example 1 was conducted exceptthat kinds of core particles, kinds and amounts of gluing agents addedin coating step with gluing agent, linear load and treating time foredge runner treatment used in the coating step with gluing agent, kindsand amounts of black pigments adhered in black pigment-adhering step,and linear load and treating time for edge runner treatment used in theblack pigment-adhering step, were changed variously, thereby obtainingblack colorants.

[0263] Meanwhile, in Example 8, the black pigments A were intermittentlyadded six times in an amount of 20 parts by weight each, to 100 parts byweight of the core particles such that the total amount of the blackpigments A added was 120 parts by weight.

[0264] In Example 14, 100 parts by weight of the black pigments B werecontinuously added to 100 parts by weight of the core particles for 100minutes.

[0265] The essential production conditions are shown in Tables 5 and 6,and various properties of the obtained black colorants are shown inTables 7 and 8.

Comparative Example 6 (Follow-up Test of Example 1 of Japanese PatentNo. 3097208)

[0266] The silica particles (core particles 1) were dispersed indistilled water at the below-mentioned blending ratio. A silane-basedcoupling agent (γ-aminopropyl triethoxysilane) was gradually added tothe obtained dispersion. After completion of addition of thesilane-based coupling agent, the dispersion was allowed to stand at 50°C. for several hours until the reaction between the silica particles andthe silane-based coupling agent was completed. Meanwhile, thetermination of the reaction between the silica particles and thesilane-based coupling agent was determined using FT-IR “MAGNA-IR”(manufactured by Nicolett Co., Ltd.). The resultant dispersion wastransferred into an attritor, and the black pigments A (carbon black)were added to the dispersion. The resultant mixture was dispersed for 12hours to conduct the reaction between the silane-based coupling agentand the black pigments A.

Dispersion Composition

[0267] Silica particles 10.0 parts by weight Distilled water 84.3 partsby weight Silane-based coupling agent 0.2 part by weight Black pigmentsA 5.0 parts by weight

[0268] Various properties of the thus obtained colored silica particlesare shown in Table 8.

Comparative Example 7 (Follow-up Test of Examples of Japanese Patent No.3105511)

[0269] 9.6 g of the silica particles (core particles 1) were placed in a500-ml round bottom flask equipped with a magnetic stirrer and aDean-Stark trap, and dried therein at 100° C. for 24 hours. 300 ml oftoluene previously dried by azeotropic distillation under a nitrogenatmosphere, and 2.96 g of a silane-based coupling agent (γ-aminopropyltriethoxysilane) were added to the dried silica particles. The obtainedsuspension was refluxed at 111° C. for 5 hours, cooled to roomtemperature, and then centrifuged at a rotating speed of about 10,000rpm. After removing a supernatant from the suspension, the resultantprecipitate was washed with 500 ml of dichloromethane, and successivelythe mixture of the precipitate and dichloromethane was centrifuged.After a supernatant was removed from the mixture, the obtained residueswere dried at 40° C. for 2.5 days in a vacuum dryer (200 mmHg), therebyobtaining 9.6 g of white particles (yield: 76%).

[0270] Next, an aqueous mixture prepared by dispersing 1.0 g of theabove silica particles containing the silane-based coupling agent and1.0 g of naphthol blue black in 40 ml of water, was placed in a roundbottom flask equipped with a magnetic stirrer, stirred therein at roomtemperature for 18 hours, and then centrifuged. The resultant residueswere dispersed in water and then centrifuged until the supernatantbecame colorless. The obtained residues were re-dispersed in water, andthen freeze-dried using a freeze dryer, thereby 0.75 g of colored silicaparticles.

[0271] Various properties of the obtained colored silica particles areshown in Table 8.

Example 18

[0272]20 g of sodium docecylbenzenesulfonate (anionic surfactant) wasadded to 2 kg of the black colorant obtained in Example 5, and theresultant mixture was stirred at 30° C. for 30 minutes using a Henschelmixer, thereby obtaining coated black colorants.

[0273] The essential production conditions are shown in Table 9, andvarious properties of the obtained coated black colorants are shown inTable 10.

Examples 19 to 23

[0274] The same procedure as defined in Example 18 was conducted exceptthat kinds of black colorants, kinds and amounts of surfactants and/orpolymeric dispersing agents, and conditions for edge runner treatmentused in the coating step, were changed variously, thereby obtainingblack colorants coated with the surfactants and/or polymeric dispersingagents.

[0275] The essential production conditions are shown in Table 9, andvarious properties of the obtained coated black colorants are shown inTable 10.

Examples 24 to 42 and Comparative Examples 8 to 17

[0276] The same procedure as defined in Example 2: Production of ink-jetprinting ink A was conducted except that kinds of black colorants werechanged variously, thereby obtaining ink-jet printing inks.

[0277] The essential production conditions are shown in Tables 11 and12, and various properties of the obtained ink-jet printing inks areshown in Tables 13 to 14.

Examples 43 to 54 and Comparative Examples 18 to 25

[0278] The same procedure as defined in Example 3 was conducted exceptthat kinds of black colorants were changed variously, thereby obtainingaqueous pigment dispersions.

[0279] The essential production conditions and various properties of theobtained aqueous pigment dispersions are shown in Tables 15 and 16.

Examples 55 to 66 and Comparative Examples 26 to 33

[0280] The same procedure as defined in Example 4 was conducted exceptthat kinds of aqueous pigment dispersions were changed variously,thereby obtaining ink-jet printing inks.

[0281] The essential production conditions and various properties of theobtained ink-jet printing inks are shown in Tables 17 and 18. TABLE 1Properties of core particles Average Kind of particle core diameterparticles Kind Shape (μm) Core Silica Spherical 0.021 particles 1 CoreSilica Granular 0.013 particles 2 Core Silica Granular 0.048 particles 3Core Silica Spherical 0.005 particles 4 Core Alumina Granular 0.098particles 5 Core Precipitated Granular 0.059 particles 6 barium sulfateCore Mn-containing Granular 0.282 particles 7 hematite particles (Mncontent: 12.6 wt. %) Properties of core particles Kind of BET specificSpecific core Sphericity surface area gravity particles (−) value (m²/g)(−) Core 1.02 196.2 2.19 particles 1 Core 1.28 256.3 2.43 particles 2Core 1.11 168.4 2.11 particles 3 Core 1.03 312.6 2.28 particles 4 Core1.31 41.3 3.65 particles 5 Core 1.22 21.3 4.15 particles 6 Core 1.36 3.85.01 particles 7 Properties of core particles Hue L* a* b* C* HidingKind of core value value value value power particles (−) (−) (−) (−)(cm²/g) Core 93.1 0.1 0.3 0.3 6 particles 1 Core 94.0 0.3 −0.1 0.3 11particles 2 Core 95.1 0.4 0.2 0.4 10 particles 3 Core 92.2 0.1 1.3 1.3 6particles 4 Core 96.3 0.1 0.2 0.1 18 particles 5 Core 91.6 0.3 1.1 1.113 particles 6 Core 22.8 5.5 1.3 5.7 1,680 particles 7

[0282] TABLE 2 Surface-treating step Additives Coating material CoreKind of Calculated Amount Calculated Amount particles core particlesKind as (wt. %) Kind as (wt. %) Core Core Sodium Al 0.5 A Al 0.49particles 8 particles 1 aluminate Core Core Aluminum Al 2.0 A Al 1.96particles 9 particles 2 sulfate Core Core Aluminum Al 5.0 A Al 4.76particles 10 particles 3 sulfate Core Core Aluminum Al 2.0 A Al 1.96particles 11 particles 4 sulfate Core Core Water SiO₂ 0.5 S SiO₂ 0.48particles 12 particles 5 glass #3 Core Core Sodium Al 2.0 A Al 1.93particles 13 particles 6 aluminate Water SiO₂ 0.5 S SiO₂ 0.47 glass #3

[0283] TABLE 3 Properties of surface-treated core particles BET specificAverage surface particle area Specific Kind of core diameter Sphericityvalue gravity particles (μm) (−) (m²/g) (−) Core 0.022 1.02 186.3 2.20particles 8 Core 0.015 1.28 211.4 2.45 particles 9 Core 0.050 1.11 129.12.18 particles 10 Core 0.005 1.03 296.4 2.31 particles 11 Core 0.0991.31 40.8 3.60 particles 12 Core 0.061 1.22 21.9 4.13 particles 13Properties of surface-treated core particles Hue L* a* b* C* Hiding Kindof core value value value value power particles (−) (−) (−) (−) (cm²/g)Core 93.1 0.1 0.1 0.1 6 particles 8 Core 94.1 0.2 0.1 0.2 10 particles 9Core 94.6 0.2 0.1 0.2 11 particles 10 Core 92.0 0.1 1.4 1.4 6 particles11 Core 93.8 0.1 0.3 0.3 21 particles 12 Core 91.0 0.4 0.8 0.9 14particles 13

[0284] TABLE 4 Properties of black pigments Average particle BETspecific Specific Blackness Black diameter surface area gravity (ΔL*value) pigments Kind Shape (μm) value (m²/g) (−) (−) Black Carbon blackGranular 0.022 134.0 1.82 16.6 pigments A (furnace black) Black Carbonblack Granular 0.045 71.2 1.95 17.1 pigments B (acetylene black) BlackAniline black Granular 0.312 56.8 1.74 15.9 pigments C

[0285] TABLE 5 Production of black colorant Coating step with gluingagent Adhesion step with black pigments Coating Amount Additives amountBlack pigments adhered Amount (cal- Amount (cal- Kind of added Edgerunner treatment culated added Edge runner treatment culated core (wt.Linear load Time as C) (wt. Linear load Time as C) Examples particlesKind part) (N/cm) (Kg/cm) (min) (wt. %) Kind part) (N/cm) (Kg/cm) (min)(wt. %) Example Core Methyl 4.0 588 60 30 1.06 A 50.0 588 60 60 32.18 5particles 1 hydrogen polysiloxane Example Core γ-amino- 10.0 588 60 601.63 B 100.0 588 60 60 48.63 6 particles 2 propyl triethoxy- silaneExample Core Methyl 2.0 294 30 30 0.13 C 100.0 588 60 90 40.01 7particles 3 triethoxy- silane Example Core Methyl 8.0 588 60 30 2.10 A120.0 735 75 60 54.35 8 particles 4 hydrogen polysiloxane Example CoreIsopropyl 1.0 441 45 20 0.74 A 100.0 588 60 60 48.92 9 particles 5triiso- stearoyl titanate Example Core Water-soluble 2.0 735 75 60 1.00B 120.0 588 60 30 54.36 10 particles 6 acrylic resin Example Core Methyl4.0 588 60 90 0.25 A 30.0 588 60 90 22.86 11 particles 8 triethoxy-silane Example Core Methyl 2.0 294 30 60 0.54 B 100.0 441 45 120 48.7712 particles 9 hydrogen polysiloxane Example 13 Core Methyl 5.0 588 6045 0.41 C 150.0 735 75 120 47.52 particles 10 trimethoxy- silane Example14 Core Methyl 5.0 588 60 20 1.05 B 100.0 588 60 30 49.56 particles 11hydrogen polysiloxane Example 15 Core Phenyl 6.0 490 50 30 2.04 A 50.0588 60 30 32.35 particles 12 triethoxy- silane Example 16 Core Dimethyl5.0 735 75 45 0.94 B 100.0 294 30 40 48.76 particles 13 dimethoxy-silane Example 17 Particles Methyl 5.0 588 60 45 1.35 C 100.0 588 60 12040.13 used in hydrogen Example 1 polysiloxane

[0286] TABLE 6 Production of black colorant Coating step with gluingagent Adhesion step with black pigments Coating Amount Additives amountBlack pigments adhered Amount (cal- Amount (cal- added Edge runnertreatment culated added Edge runner treatment culated Comparative Kindof core (wt. Linear load Time as C) (wt. Linear load Time as C) Examplesparticles Kind part) (N/cm) (Kg/cm) (min) (wt. %) Kind part) (N/cm)(Kg/cm) (min) (wt. %) Comparative Core — — — — — — A 50.0 588 60 6032.30 Example 1 particles 1 Comparative Core Methyl 0.005 588 60 30 1 ×10⁻³ A 50.0 588 60 60 32.15 Example 2 particles 1 hydrogen poly-siloxane Comparative Core Methyl 4.0 588 60 30 1.07 A 0.5 588 60 60 0.48Example 3 particles 1 hydrogen poly- siloxane Comparative Core Methyl4.0 588 60 30 1.06 A 750.0 588 60 60 87.79 Example 4 particles 1hydrogen poly- siloxane Comparative Core Methyl 4.0 588 60 30 1.06 A50.0 588 60 60 32.22 Example 5 particles 7 hydrogen poly- siloxane

[0287] TABLE 7 Properties of black colorant Average particle BETspecific Specific Blackness Tinting Light resistance Degree ofdesorption diameter Sphericity surface area gravity (L* value) strength(ΔE* value) of black pigments Examples (μm) (−) value (m²/g) (−) (−) (%)(−) (−) Example 5 0.023 1.02 152.1 2.04 17.9 127 1.8 5 Example 6 0.0181.28 180.5 2.13 18.7 136 1.6 5 Example 7 0.052 1.11 98.3 1.92 17.0 1221.9 5 Example 8 0.009 1.03 198.6 1.99 17.2 140 1.8 5 Example 9 0.1001.31 50.4 2.73 17.3 136 1.5 4 Example 10 0.063 1.22 37.2 2.93 19.0 1361.4 4 Example 11 0.024 1.03 156.6 2.08 17.2 136 1.0 5 Example 12 0.0201.28 170.9 2.19 19.1 130 1.6 5 Example 13 0.055 1.12 80.1 1.91 16.9 1241.5 5 Example 14 0.008 1.03 211.4 2.03 17.3 135 1.4 5 Example 15 0.1031.31 49.5 2.93 20.8 128 1.3 5 Example 16 0.064 1.22 35.7 2.99 20.2 1291.1 5 Example 17 0.026 1.06 106.3 2.01 17.0 123 1.8 5

[0288] TABLE 8 Properties of black colorant Average particle BETspecific Specific Blackness Tinting Light resistance Degree ofdesorption Comparative diameter Sphericity surface area gravity (L*value) strength (ΔE* value) of black pigments Examples (μm) (−) value(m²/g) (−) (−) (%) (−) (−) Comparative 0.022 1.06 172.3 2.07 23.0 1026.3 1 Example 1 Comparative 0.022 1.05 160.5 2.07 22.8 105 6.0 2 Example2 Comparative 0.021 1.02 191.2 2.14 34.5 101 1.7 — Example 3 Comparative0.033 1.08 141.3 1.86 16.8 197 5.5 1 Example 4 Comparative 0.283 1.3914.8 3.87 17.4 118 3.5 1 Example 5 Comparative 0.021 1.02 163.8 2.0518.0 108 6.9 1 Example 6 Comparative 0.021 1.02 180.1 2.14 23.4 95 11.2— Example 7

[0289] TABLE 9 Production of surface-coated black colorant Coating stepwith surfactant Coating Additives amount Kind of Amount Treating(calculated black added temperature Treating time as C) Examplescolorant Kind (wt. part) (° C.) (min) (wt. %) Example 18 Example 5Sodium 1.0 30 30 0.61 dodecylbenzene sulfonate Example 19 Example 7Sodium acrylate 2.0 25 30 0.70 Example 20 Example 9 Sodium 1.0 30 200.48 laurylsulfate Example 21 Example 10 Nonylphenyl 5.0 30 30 3.69polyethylene glycol ether Example 22 Example 12 Sodium 1.0 25 20 0.60dodecylbenzene sulfonate Example 23 Example 14 Sodium 2.0 35 30 1.21dodecylbenzene sulfonate

[0290] TABLE 10 Properties of black colorant BET specific Averagesurface Light particle area Specific Blackness Tinting resistancediameter Sphericity value gravity (L* value) strength (ΔE* value)Examples (μm) (−) (m²/cr) (−) (−) (%) (−) Example 18 0.023 1.02 145.62.02 18.0 128 1.7 Example 19 0.052 1.11 94.5 1.90 17.2 122 1.8 Example20 0.100 1.31 48.2 2.71 17.4 137 1.6 Example 21 0.064 1.22 34.3 2.8419.3 136 1.3 Example 22 0.020 1.28 168.0 2.18 19.2 131 1.5 Example 230.009 1.03 176.4 2.01 17.5 136 1.3

[0291] TABLE 11 Production of black ink-jet printing ink Black colorantColloidal silica Amount Amount blended blended (wt. (wt. Examples Kindpart) Kind part) Example 24 Example 5 5.0 — — Example 25 Example 6 5.0 —— Example 26 Example 7 5.0 — — Example 27 Example 8 5.0 — — Example 28Example 9 5.0 — — Example 29 Example 10 5.0 — — Example 30 Example 115.0 — — Example 31 Example 12 5.0 — — Example 32 Example 13 5.0 — —Example 33 Example 14 5.0 — — Example 34 Example 15 5.0 — — Example 35Example 16 5.0 — — Example 36 Example 17 5.0 — — Example 37 Example 185.0 — — Example 38 Example 19 5.0 — — Example 39 Example 20 5.0 — —Example 40 Example 21 5.0 — — Example 41 Example 22 5.0 — — Example 42Example 23 5.0 — —

[0292] TABLE 12 Production of black ink-jet printing ink Black colorantColloidal silica Amount Amount Comparative blended blended Examples Kind(wt. part) Kind (wt. part) Comparative Black 5.0 Core 10.0 Example 8pigments A particles 1 Comparative Black 5.0 Core 10.0 Example 9pigments B particles 7 Comparative Black 5.0 Core 10.0 Example 10pigments C particles 1 Comparative Comparative 5.0 — — Example 11Example 1 Comparative Comparative 5.0 — — Example 12 Example 2Comparative Comparative 5.0 — — Example 13 Example 3 ComparativeComparative 5.0 — — Example 14 Example 4 Comparative Compartive 5.0 — —Example 15 Example 5 Comparative Comparative 5.0 — — Example 16 Example6 Comparative Comparative 5.0 — — Example 17 Example 7

[0293] TABLE 13 Properties of black ink-jet printing ink Dispersionstability Percentage of change in Dispersed diperesed Light particleVisual particle Blackness resistance Anti-clogging diameter observationdiameter (L* value) (ΔE* value) property Examples (μm) (−) (%) (−) (−)(−) Example 24 0.03 5 6.6 18.0 1.8 5 Example 25 0.03 5 6.8 18.7 1.5 5Example 26 0.06 5 6.4 17.2 1.8 5 Example 27 0.02 5 6.5 17.4 1.8 5Example 28 0.13 4 8.8 17.4 1.5 4 Example 29 0.08 4 9.2 19.2 1.4 4Example 30 0.03 5 5.6 17.3 1.0 5 Example 31 0.03 5 5.3 19.4 1.5 5Example 32 0.06 5 5.1 17.0 1.4 5 Example 33 0.02 5 5.4 17.4 1.5 5Example 34 0.13 4 8.4 20.9 1.3 4 Example 35 0.08 4 8.9 20.4 1.0 4Example 36 0.03 5 6.6 17.1 1.7 5 Example 37 0.03 5 4.4 18.2 1.6 5Example 38 0.03 5 4.5 17.3 1.7 5 Example 39 0.12 5 6.7 17.6 1.5 5Example 40 0.08 5 7.5 19.5 1.3 5 Example 41 0.03 5 3.9 19.4 1.3 5Example 42 0.02 5 4.0 17.5 1.4 5

[0294] TABLE 14 Properties of black ink-jet printing ink Dispersionstability Percentage of change in Dispersed despersed Light particleVisual particle Blackness resistance Anti-clogging Comparative diameterobservation diamerter (L* value) (ΔE* value) property Examples (μm) (−)(%) (−) (−) (−) Comparative 0.08 1 18.8 17.3 6.8 2 Example 8 Comparative0.14 1 20.1 18.0 6.6 2 Example 9 Comparative 0.66 1 24.9 17.2 8.9 1Example 10 Comparative 0.22 1 18.0 23.4 6.3 2 Example 11 Comparative0.21 2 17.1 23.0 6.1 2 Example 12 Comparative 0.07 3 13.5 35.1 1.8 3Example 13 Comparative 0.18 2 17.0 17.2 5.4 2 Example 14 Comparative0.22 2 22.2 17.9 3.4 1 Example 15 Comparative 0.16 1 15.3 18.3 6.7 2Example 16 Comparative 0.08 3 8.6 23.6 11.1 3 Example 17

[0295] TABLE 15 Properties of aqueous pigment dispersion Dispersionstability Production of aqueous pigment dispersion Percentage of Blackcolorant Colloidal silica change in Amount Amount Dispersed dispersedblended blended particle Visual particle (wt. (wt. diameter observationdiameter Examples Kind part) Kind part) (μm) (−) (%) Example 43 Example5 20.0 — — 0.06 5 8.1 Example 44 Example 7 20.0 — — 0.08 5 8.4 Example45 Example 9 20.0 — — 0.16 4 10.6 Example 46 Example 10 20.0 — — 0.10 410.4 Example 47 Example 12 20.0 — — 0.06 5 6.6 Example 48 Example 1420.0 — — 0.05 5 7.3 Example 49 Example 18 20.0 — — 0.05 5 5.1 Example 50Example 19 20.0 — — 0.05 5 5.2 Example 51 Example 20 20.0 — — 0.13 5 7.6Example 52 Example 21 20.0 — — 0.09 5 8.1 Example 53 Example 22 20.0 — —0.05 5 4.8 Example 54 Example 23 20.0 — — 0.04 5 5.0

[0296] TABLE 16 Properties of aqueous pigment dispersion Dispertionstability Production of aqueous pigment dispersion Percentage of Blackcolorant Colloidal silica change in Amount Amount Dispersed dispersedblended blended particle Visual particle Comparative (wt. (wt. diameterobservation diameter Examples Kind part) Kind part) (μm) (−) (%)Comparative Black 10.0 Core 10.0 0.18 1 21.6 Example 18 pigments Aparticles 1 Comparative Comparative 20.0 — — 0.31 1 21.5 Example 19Example 1 Comparative Comparative 20.0 — — 0.33 2 21 2 Example 20Example 2 Comparative Comparative 20.0 — — 0.23 3 17.3 Example 21Example 3 Comparative Comparative 20.0 — — 0.26 2 21.2 Example 22Example 4 Comparative Comparative 20.0 — — 0.28 2 26.3 Example 23Example 5 Comparative Comparative 20.0 — — 0.24 1 18.6 Example 24Example 6 Comparative Comparative 20.0 — — 0.19 3 13.8 Example 25Example 7

[0297] TABLE 17 Properties of aqueous pigment dispersion Dispersionstability Percentage of change in Production of ink-jet printing inkDispersed dispersed Light Aqueous pigment dispersion particle Visualparticle Blackness resistance Anti-clogging Amount blended diameterobservation diameter (L* value) (ΔE* value) property Examples Kind (wt.part) (μm) (−) (%) (−) (−) (−) Example 55 Example 43 25.0 0.02 5 6.418.0 1.7 5 Example 56 Example 44 25.0 0.05 5 6.3 17.3 1.6 5 Example 57Example 45 25.0 0.10 4 8.3 17.3 1.5 4 Example 58 Example 46 25.0 0.06 48.6 19.0 1.4 4 Example 59 Example 47 25.0 0.02 5 5.2 19.2 1.4 5 Example60 Example 48 25.0 0.02 5 5.1 17.8 1.4 5 Example 61 Example 49 25.0 0.025 4.2 18.1 1.5 5 Example 62 Example 50 25.0 0.03 5 4.2 17.3 1.6 5Example 63 Example 51 25.0 0.09 5 6.5 17.5 1.4 5 Example 64 Example 5225.0 0.05 5 7.1 19.3 1.2 5 Example 65 Example 53 25.0 0.02 5 3.8 19.11.2 5 Example 66 Example 54 25.0 0.03 5 3.6 17.6 1.1 5

[0298] TABLE 18 Properties of aqueous pigment dispersion Dispersionstability Percentage of change in Production of ink-jet printing inkDispersed dispersed Light Aqueous pigment dispersion particle Visualparticle Blackness resistance Anti-clogging Comparative Amount blendeddiameter observation diameter (L* value) (ΔE* value) property ExamplesKind (wt. part) (μm) (−) (%) (−) (−) (−) Comparative Comparative 25.00.08 1 18.4 18.7 6.7 2 Example 26 Example 18 Comparative Comparative25.0 0.20 1 17.8 23.3 6.2 2 Example 27 Example 19 ComparativeComparative 25.0 0.19 2 17.0 22.8 6.1 2 Example 28 Example 20Comparative Comparative 25.0 0.06 3 13.3 35.0 1.8 3 Example 29 Example21 Comparative Comparative 25.0 0.17 2 16.8 17.2 5.3 2 Example 30Example 22 Comparative Comparative 25.0 0.21 2 21.9 17.8 3.3 1 Example31 Example 23 Comparative Comparative 25.0 0.15 1 15.1 18.1 6.5 2Example 32 Example 24 Comparative Comparative 25.0 0.07 3 8.5 23.5 11.03 Example 33 Example 25

What is claimed is:
 1. A black colorant for ink-jet printing ink, havingan average particle diameter of 0.001 to 0.15 μm, comprising: extenderpigments as core particles; a gluing agent-coating layer formed on atleast a part of the surface of said core particle; and a black pigmentcoat uniformly formed on at least a part of said gluing agent-coatinglayer.
 2. A black colorant according to claim 1, which further has a BETspecific surface area value of 15 to 1,000 m²/g, a specific gravity of1.3 to 3.0 and a blackness L* value of not more than 22.0.
 3. A blackcolorant according to claim 1, wherein said gluing agent is at least onematerial selected from the group consisting of organosilicon compoundsand coupling agents.
 4. A black colorant according to claim 1, whereinthe amount of said black pigment coat is 1 to 500 parts by weight basedon 100 parts by weight of said extender pigments.
 5. A black colorantaccording to claim 1, which further comprises an outer coating layerformed on at least a part of said black pigment coat, comprising atleast one material selected from the group consisting of anionicsurfactants, nonionic surfactants, cationic surfactants and polymericdispersing agents.
 6. A black colorant according to claim 5, wherein theamount of said outer coating layer is 0.1 to 10.0% by weight, calculatedas C, based on the weight of the black colorant.
 7. A black colorantaccording to claim 1, wherein a coating layer comprising at least onecompound selected from the group consisting of hydroxides of aluminum,oxides of aluminum, hydroxides of silicon and oxides of silicon, isformed between the surface of said core particle and the gluingagent-coating layer.
 8. A black colorant according to claim 7, whereinthe amount of said coating layer comprising at least one compoundselected from the group consisting of hydroxides of aluminum, oxides ofaluminum, hydroxides of silicon and oxides of silicon, is 0.01 to 20% byweight, calculated as Al, SiO₂ or a sum of Al and SiO₂, based on theweight of the core particles coated therewith.
 9. A black colorant forink-jet printing ink, having an average particle diameter of 0.001 to0.15 μm, a BET specific surface area value of 15 to 1,000 m²/g, aspecific gravity of 1.3 to 3.0 and a blackness L* value of not more than22.0, comprising: extender pigments as core particles; a gluingagent-coating layer formed on at least a part of the surface of saidcore particle; and a black pigment coat uniformly formed on at least apart of said gluing agent-coating layer in the amount of 1 to 500 partsby weight based on 100 parts by weight of said extender pigments.
 10. Ablack colorant for ink-jet printing ink, having an average particlediameter of 0.001 to 0.15 μm, comprising: extender pigments as coreparticles; a gluing agent-coating layer formed on at least a part of thesurface of said core particle; a black pigment coat uniformly formed onat least a part of said gluing agent-coating layer; and an outer coatinglayer formed on at least a part of said black pigment coat, comprisingat least one material selected from the group consisting of anionicsurfactants, nonionic surfactants, cationic surfactants and polymericdispersing agents.
 11. A black colorant for ink-jet printing ink, havingan average particle diameter of 0.001 to 0.15 μm, comprising: extenderpigments as core particles; a coating layer formed on at least a part ofthe surface of said core particle, comprising at least one compoundselected from the group consisting of hydroxides of aluminum, oxides ofaluminum, hydroxides of silicon and oxides of silicon; a gluingagent-coating layer formed on at least a part of the surface of saidcoating layer; a black pigment coat uniformly formed on at least a partof said gluing agent-coating layer.
 12. A black colorant for ink-jetprinting ink, having an average particle diameter of 0.001 to 0.15 μm,comprising: extender pigments as core particles; a coating layer formedon at least a part of the surface of said core particle, comprising atleast one compound selected from the group consisting of hydroxides ofaluminum, oxides of aluminum, hydroxides of silicon and oxides ofsilicon, a gluing agent-coating layer formed on at least a part of thesurface of said coating layer; a black pigment coat uniformly formed onat least a part of said gluing agent-coating layer; and an outer coatinglayer formed on at least a part of said black pigment coat, comprisingat least one material selected from the group consisting of anionicsurfactants, nonionic surfactants, cationic surfactants and polymericdispersing agents.
 13. An ink-jet printing ink comprising the blackcolorant as defined in claim 1 and an ink base solution.
 14. An ink-jetprinting ink according to claim 13, wherein the amount of said blackcolorant is 1 to 20% by weight based on the weight of the ink basesolution.
 15. An ink-jet printing ink comprising the black colorant asdefined in claim 9, 10, 11 or 12 and an ink base solution the amount ofsaid black colorant being 1 to 20% by weight based on the weight of theink base solution.
 16. An aqueous pigment dispersion comprising 10 to40% by weight of the black colorant as defined in claim 1, and a basesolution for the aqueous pigment dispersion.
 17. An ink-jet printing inkcomprising the aqueous pigment dispersion as defined in claim 16, adispersant and water.